Preserve mask when copying wxBitmapRefData to avoid crashes

This crash was introduced in 2d15218c9d
and could happens inside wxBitmap::MSWBlendMaskWithAlpha() because the
code checked for a mask and alpha, but the mask could be lost after
AllocExclusive().

In practice, this happened e.g. when using 16-bit color as is the case
for Windows 7 Hyper-V VMs.

Closes https://github.com/wxWidgets/wxWidgets/pull/1695

src/msw/bitmap.cpp

@@ -223,10 +223,6 @@ wxBitmapRefData::wxBitmapRefData(const wxBitmapRefData& data)
 {
     Init();
 
-    // (deep) copy the mask if present
-    if (data.m_bitmapMask)
-        m_bitmapMask = new wxMask(*data.m_bitmapMask);
-
 #if wxUSE_WXDIB
     wxASSERT_MSG( !data.m_dib,
                     wxT("can't copy bitmap locked for raw access!") );
@@ -261,6 +257,11 @@ wxBitmapRefData::wxBitmapRefData(const wxBitmapRefData& data)
         }
     }
 #endif // wxUSE_WXDIB
+
+    // Ensure this is done after the block above otherwise if the color depth didn't match we'll lose the mask
+    // (deep) copy the mask if present
+    if (data.m_bitmapMask)
+        m_bitmapMask = new wxMask(*data.m_bitmapMask);
 }
 
 void wxBitmapRefData::Free()