mi: Use GC clipregion instead of drawable in miDoCopy/miCopyArea

As discussed in issue #829 the "mi: Shortcut miDoCopy/miCopyArea based
on clipList" change leads to pointer-trails (area under pointer not
restored when it moves) when using a software cursor.

Checking pGC->pCompositeClip instead of pDstDrawable->clipList fixes
this problem.

Fixes: #829
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
3 jobs for sw-pointer-trails-fix in 9 minutes and 51 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Docker Image
passed #477729
debian-testing

00:00:31

 
  Build And Test
passed #477730
autotools-build-and-test

00:09:20

passed #477731
meson-build-and-test

00:01:30