Don't initialize alpha twice when loading wxImage from resources.

Calling InitAlpha() when we already had loaded alpha from the resource data
results in an assert. Fix this by only initializing alpha if don't have it
yet.

Closes #14643.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@72471 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/image.cpp

@@ -2306,7 +2306,10 @@ static wxImage LoadImageFromResource(const wxString &name, wxBitmapType type)
         image.SetMaskColour(0xc0, 0xc0, 0xc0);
     }
 
-    image.InitAlpha();
+    // We could have already loaded alpha from the resources, but if not,
+    // initialize it now using the mask.
+    if ( !image.HasAlpha() )
+        image.InitAlpha();
 
     return image;
 }