Fix error message for failure to load PNG from resources

Remove the extraneous comma which replaced the resource name with the
second part of the error message, resulting in confusing output.

See #18773.

src/msw/gdiimage.cpp

@@ -629,7 +629,7 @@ bool wxPNGResourceHandler::LoadFile(wxBitmap *bitmap,
     *bitmap = wxBitmap::NewFromPNGData(pngData, pngSize);
     if ( !bitmap->IsOk() )
     {
-        wxLogError(wxS("Couldn't load resource bitmap \"%s\" as a PNG. "),
+        wxLogError(wxS("Couldn't load resource bitmap \"%s\" as a PNG. ")
                    wxS("Have you registered PNG image handler?"),
                    name);