gtk3: glitches because yours truly cannot tell x from y

(cherry picked from commit 2ca429e7)

(cherry picked from commit 9401a065)

Change-Id: I3b8620a4d8bffeb5e0558c35cb3a063238c12ba5
Reviewed-on: https://gerrit.libreoffice.org/20311Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Stahl <mstahl@redhat.com>

vcl/headless/svpgdi.cxx

@@ -144,11 +144,11 @@ namespace
         double x1, y1, x2, y2;
 
         cairo_clip_extents(cr, &x1, &y1, &x2, &y2);
-        extents.x = x1, extents.y = x2, extents.width = x2-x1, extents.height = y2-y1;
+        extents.x = x1, extents.y = y1, extents.width = x2-x1, extents.height = y2-y1;
         cairo_region_t *region = cairo_region_create_rectangle(&extents);
 
         cairo_fill_extents(cr, &x1, &y1, &x2, &y2);
-        extents.x = x1, extents.y = x2, extents.width = x2-x1, extents.height = y2-y1;
+        extents.x = x1, extents.y = y1, extents.width = x2-x1, extents.height = y2-y1;
         cairo_region_intersect_rectangle(region, &extents);
 
         cairo_region_get_extents(region, &extents);