Make it easier to catch code that assumes SalBitmaps are created pre-cleared

In a DBG_UTIL build fill the maContextBuffer and maUserBuffer of a
QuartzSalBitmap with an easily recognized pattern. Helps catch
situations where by coincidence they appear pre-filled with zeros most
of the time and almost everything usually looks fine.

Or is the QuartzSalBitmap implementation wrong, and SalBitmaps
*should* be created filled with zeros?

Change-Id: Ib5207779f2a47b9b7e539d8646b4128fea0ec150

vcl/quartz/salbmp.cxx

@@ -211,6 +211,10 @@ bool QuartzSalBitmap::CreateContext()
         try
         {
             maContextBuffer.reset( new sal_uInt8[ mnHeight * nContextBytesPerRow ] );
+#ifdef DBG_UTIL
+            for (size_t i = 0; i < mnHeight * nContextBytesPerRow; i++)
+                maContextBuffer.get()[i] = (i & 0xFF);
+#endif
 
             if( !bSkipConversion )
                 ConvertBitmapData( mnWidth, mnHeight,
@@ -261,6 +265,10 @@ bool QuartzSalBitmap::AllocateUserData()
     {
         if( mnBytesPerRow )
             maUserBuffer.reset( new sal_uInt8[mnBytesPerRow * mnHeight] );
+#ifdef DBG_UTIL
+        for (size_t i = 0; i < mnBytesPerRow * mnHeight; i++)
+            maUserBuffer.get()[i] = (i & 0xFF);
+#endif
     }
     catch( const std::bad_alloc& )
     {