flush surface for all backends

Change-Id: Ifa6f7f9a816096bfe9f44baca17b34e54b83a5c6

vcl/unx/generic/gdi/cairotextrender.cxx

@@ -338,6 +338,7 @@ void CairoTextRender::DrawServerFontLayout( const ServerFontLayout& rLayout )
         aI = aNext;
     }
 
+    cairo_surface_flush(cairo_get_target(cr));
     drawSurface(cr);
     cairo_destroy(cr);
 }

vcl/unx/generic/gdi/openglx11cairotextrender.cxx

@@ -65,7 +65,6 @@ void OpenGLX11CairoTextRender::drawSurface(cairo_t* cr)
     cairo_surface_t* pSurface = cairo_get_target(cr);
     int nWidth = cairo_image_surface_get_width( pSurface );
     int nHeight = cairo_image_surface_get_height( pSurface );
-    cairo_surface_flush( pSurface );
     unsigned char *pSrc = cairo_image_surface_get_data( pSurface );
 
     // XXX: lfrb: GLES 2.0 doesn't support GL_UNSIGNED_INT_8_8_8_8_REV