Fix creating wxMask image from raw data

In the function wxMask::OSXCreate() to create a mask image, data copying
from the supplied memory buffer was not actually implemented and therefore
created mask was invalid.

Closes #18513.

include/wx/osx/bitmap.h

@@ -66,7 +66,7 @@ public:
 
     WXHBITMAP GetHBITMAP() const ;
 
-    // implementation helper only : construct a mask from a 32 bit memory buffer
+    // implementation helper only : construct a mask from a 8 bpp memory buffer
     bool OSXCreate(const wxMemoryBuffer& buf, int width , int height , int bytesPerRow ) ;
 
 protected: