Fixes logically dead code (Coverity)

Fixes reported logically dead codes by Coverity

* image.cpp: Doesn't really need any modification. But to remove the bug
report then we have to move the MAX call away from the for loop
statement.

* rasterizer_gles3.cpp: Removes unnecessary elif condition since it is
checked earlier in the function

* collada.cpp: If stamement never reached due to macro ERR_CONTINUE does
the same.

* navigation_mesh.cpp: Variables should always be null - however, also
checked for the very same condition in their function call. Leaving this
for review (whether the function call is necessary or not)

* path_editor_plugin.cpp: If cancel is true, then it should restore the
edited value to the original provided.
http://docs.godotengine.org/en/3.0/classes/class_editorspatialgizmo.html#class-editorspatialgizmo-commit-handle

* spatial_editor_gizmos.cpp: the very condition of i >= 3 is
predetermined in the if case right before it. Thus case 1 is always '1'
and case 2 is always '-1'

* grid_map_editor.cpp: Same as above in spatial_editor_gizmos.cpp

* voxel_light_baker.cpp: Same as above in spatial_editor_gizmos.cpp

* visual_server.cpp: Same as above in spatial_editor_gizmos.cpp

* visual_script_expression.cpp: char '-' is already true in the switch
case mechanism. Thus it can never reach to default case.

* particles.cpp: Case 'PARAM_MAX' is unreachable due to index checking
right before the switch execution.

* shader_language.cpp: Invalid index is handled in switch default case.
`type < TYPE_FLOAT && type > TYPE_VEC4` -> `(type < TYPE_FLOAT || type > TYPE_VEC4`)
Fixes the "always false problem" in TODO comment.

4 files changed, 20 insertions, 33 deletions

diff --git a/editor/collada/collada.cpp b/editor/collada/collada.cpp
index 4ce57d7f63..734229d014 100644
--- a/editor/collada/collada.cpp
+++ b/editor/collada/collada.cpp
@@ -2266,10 +2266,8 @@ void Collada::_merge_skeletons2(VisualScene *p_vscene) {
 				}
 				node = node->parent;
 			}
-			ERR_CONTINUE(!sk);
 
-			if (!sk)
-				continue; //bleh
+			ERR_CONTINUE(!sk);
 
 			if (!skeleton) {
 				skeleton = sk;
diff --git a/editor/plugins/navigation_mesh_generator.cpp b/editor/plugins/navigation_mesh_generator.cpp
index 5d4e5520f4..0537c5c31f 100644
--- a/editor/plugins/navigation_mesh_generator.cpp
+++ b/editor/plugins/navigation_mesh_generator.cpp
@@ -280,26 +280,20 @@ void NavigationMeshGenerator::bake(Ref<NavigationMesh> p_nav_mesh, Node *p_node)
 
 		_build_recast_navigation_mesh(p_nav_mesh, &ep, hf, chf, cset, poly_mesh, detail_mesh, vertices, indices);
 
-		if (hf) {
-			rcFreeHeightField(hf);
-			hf = 0;
-		}
-		if (chf) {
-			rcFreeCompactHeightfield(chf);
-			chf = 0;
-		}
-		if (cset) {
-			rcFreeContourSet(cset);
-			cset = 0;
-		}
-		if (poly_mesh) {
-			rcFreePolyMesh(poly_mesh);
-			poly_mesh = 0;
-		}
-		if (detail_mesh) {
-			rcFreePolyMeshDetail(detail_mesh);
-			detail_mesh = 0;
-		}
+		rcFreeHeightField(hf);
+		hf = 0;
+
+		rcFreeCompactHeightfield(chf);
+		chf = 0;
+
+		rcFreeContourSet(cset);
+		cset = 0;
+
+		rcFreePolyMesh(poly_mesh);
+		poly_mesh = 0;
+
+		rcFreePolyMeshDetail(detail_mesh);
+		detail_mesh = 0;
 	}
 	ep.step(TTR("Done!"), 11);
 }
diff --git a/editor/plugins/path_editor_plugin.cpp b/editor/plugins/path_editor_plugin.cpp
index 056219a575..6dde639c54 100644
--- a/editor/plugins/path_editor_plugin.cpp
+++ b/editor/plugins/path_editor_plugin.cpp
@@ -167,18 +167,12 @@ void PathSpatialGizmo::commit_handle(int p_idx, const Variant &p_restore, bool p
 
 	Vector3 ofs;
 
-	if (p_cancel) {
-
-		return;
-	}
-
 	if (t == 0) {
-
 		if (p_cancel) {
-
 			c->set_point_in(p_idx, p_restore);
 			return;
 		}
+
 		ur->create_action(TTR("Set Curve In Position"));
 		ur->add_do_method(c.ptr(), "set_point_in", idx, c->get_point_in(idx));
 		ur->add_undo_method(c.ptr(), "set_point_in", idx, p_restore);
@@ -186,10 +180,11 @@ void PathSpatialGizmo::commit_handle(int p_idx, const Variant &p_restore, bool p
 
 	} else {
 		if (p_cancel) {
-
 			c->set_point_out(idx, p_restore);
+
 			return;
 		}
+
 		ur->create_action(TTR("Set Curve Out Position"));
 		ur->add_do_method(c.ptr(), "set_point_out", idx, c->get_point_out(idx));
 		ur->add_undo_method(c.ptr(), "set_point_out", idx, p_restore);
diff --git a/editor/spatial_editor_gizmos.cpp b/editor/spatial_editor_gizmos.cpp
index 8c90d86b9e..a3c4b73ae4 100644
--- a/editor/spatial_editor_gizmos.cpp
+++ b/editor/spatial_editor_gizmos.cpp
@@ -4052,9 +4052,9 @@ SpatialEditorGizmos::SpatialEditorGizmos() {
 				for (int k = 0; k < 3; k++) {
 
 					if (i < 3)
-						face_points[j][(i + k) % 3] = v[k] * (i >= 3 ? -1 : 1);
+						face_points[j][(i + k) % 3] = v[k];
 					else
-						face_points[3 - j][(i + k) % 3] = v[k] * (i >= 3 ? -1 : 1);
+						face_points[3 - j][(i + k) % 3] = -v[k];
 				}
 			}
 			//tri 1