Fix warnings about uninitialized vars [-Wsometimes-uninitialized]

Fixes the following Clang 7 warnings:
```
drivers/gles3/rasterizer_scene_gles3.cpp:1260:10: warning: variable 'target' is used uninitialized whenever switch case is taken [-Wsometimes-uninitialized]
drivers/gles3/rasterizer_scene_gles3.cpp:1280:10: warning: variable 'target' is used uninitialized whenever switch case is taken [-Wsometimes-uninitialized]
drivers/gles3/rasterizer_scene_gles3.cpp:1281:10: warning: variable 'target' is used uninitialized whenever switch case is taken [-Wsometimes-uninitialized]
drivers/gles3/rasterizer_scene_gles3.cpp:1282:10: warning: variable 'target' is used uninitialized whenever switch case is taken [-Wsometimes-uninitialized]
drivers/gles3/rasterizer_scene_gles3.cpp:1286:5: warning: variable 'target' is used uninitialized whenever switch default is taken [-Wsometimes-uninitialized]
editor/editor_properties_array_dict.cpp:982:15: warning: variable 'change_index' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
editor/editor_properties.cpp:2655:6: warning: variable 'lt' is used uninitialized whenever switch default is taken [-Wsometimes-uninitialized]
editor/settings_config_dialog.cpp:367:11: warning: variable 'current_search_box' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
```

1 files changed, 1 insertions, 1 deletions

diff --git a/editor/editor_properties_array_dict.cpp b/editor/editor_properties_array_dict.cpp
index 4e638cb4ac..24360813a2 100644
--- a/editor/editor_properties_array_dict.cpp
+++ b/editor/editor_properties_array_dict.cpp
@@ -969,7 +969,7 @@ void EditorPropertyDictionary::update_property() {
 				pc->add_child(add_vbox);
 			}
 			prop->set_object_and_property(object.ptr(), prop_name);
-			int change_index;
+			int change_index = 0;
 
 			if (i < amount) {
 				String cs = key.get_construct_string();