Clarify wxButton::AdjustForBitmapSize() semantics in wxMSW.

This method should only be called if we do have an image, assert (instead of
silently returning) if it's called when we don't.

Also explain in a comment why do we need to call CacheBestSize() only when we
have an image in DoGetBestSize().

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66890 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/button.cpp

@@ -531,8 +531,7 @@ void wxButton::SetLabel(const wxString& label)
 
 void wxButton::AdjustForBitmapSize(wxSize &size) const
 {
-    if ( !m_imageData )
-        return;
+    wxCHECK_RET( m_imageData, wxT("shouldn't be called if no image") );
 
     // account for the bitmap size
     const wxSize sizeBmp = m_imageData->GetBitmap(State_Normal).GetSize();
@@ -614,6 +613,8 @@ wxSize wxButton::DoGetBestSize() const
     {
         AdjustForBitmapSize(size);
 
+        // The best size has changed so even if it had been already cached by
+        // ComputeBestSize() call above we still need to update it.
         CacheBestSize(size);
     }