Round frame sizes up, not down in wxOSX

On Retina display macs, those values can contain halves.  If you round
them down, you end up cutting off content (e.g. cutting off the last
letter in a text label).

Closes https://github.com/wxWidgets/wxWidgets/pull/1905

src/osx/cocoa/window.mm

@@ -3448,8 +3448,8 @@ void wxWidgetCocoaImpl::GetBestRect( wxRect *r ) const
         [m_osxView sizeToFit];
         NSRect best = [m_osxView frame];
         [m_osxView setFrame:former];
-        r->width = (int)best.size.width;
-        r->height = (int)best.size.height;
+        r->width = (int)ceil(best.size.width);
+        r->height = (int)ceil(best.size.height);
     }
 }