tdf#124042: If mrContext is zero, calling Core Graphics APIs on it is futile

If mrContext is zero, the CG calls using it won't do anything and will
cause "invalid context" warnings when running under Xcode. So just
return early. Such calls to drawPolyPolygon() are apparently not
essential but accidental and of no real use. Possibly related to bogus
"focus" indicator painting. Which does not make sense on iOS as we
aren't drawing to any actual "windows" with "focus".

Change-Id: Icc4a768d8b255c09a8972551443ce59f4ad56089

vcl/quartz/salgdicommon.cxx

@@ -966,6 +966,11 @@ bool AquaSalGraphics::drawPolyPolygon(
     const basegfx::B2DPolyPolygon& rPolyPolygon,
     double fTransparency)
 {
+#ifdef IOS
+    if (!mrContext)
+        return true;
+#endif
+
     // short circuit if there is nothing to do
     if( rPolyPolygon.count() == 0 )
         return true;