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.

1 files changed, 4 insertions, 1 deletions

diff --git a/core/image.cpp b/core/image.cpp
index 2ac8ffea56..9f03892e74 100644
--- a/core/image.cpp
+++ b/core/image.cpp
@@ -366,6 +366,8 @@ int Image::get_mipmap_count() const {
 template <uint32_t read_bytes, bool read_alpha, uint32_t write_bytes, bool write_alpha, bool read_gray, bool write_gray>
 static void _convert(int p_width, int p_height, const uint8_t *p_src, uint8_t *p_dst) {
 
+	uint32_t max_bytes = MAX(read_bytes, write_bytes);
+
 	for (int y = 0; y < p_height; y++) {
 		for (int x = 0; x < p_width; x++) {
 
@@ -379,7 +381,8 @@ static void _convert(int p_width, int p_height, const uint8_t *p_src, uint8_t *p
 				rgba[1] = rofs[0];
 				rgba[2] = rofs[0];
 			} else {
-				for (uint32_t i = 0; i < MAX(read_bytes, write_bytes); i++) {
+
+				for (uint32_t i = 0; i < max_bytes; i++) {
 
 					rgba[i] = (i < read_bytes) ? rofs[i] : 0;
 				}