Jamey Sharp authored May 19, 2010 and Keith Packard committed May 23, 2010

ActivateDevice was ignoring errors from DeviceCursorInitialize, so
cursor-related calls failed later. Jeremy Huddleston saw that crash in
miPointerConstrainCursor, while with Xvfb I saw it in
miSpriteRealizeCursor.

miDCDeviceCleanup frees any non-NULL GCs. miDCDeviceInitialize calls
Cleanup on any failure, but if it failed early then some of the pointers
in the miDCBufferPtr were garbage. Switch from malloc to calloc to
ensure everything's initialized safely first.

With these two fixes, if CreateGC fails then the server gracefully fails
in FatalError instead of segfaulting.

Signed-off-by: Jamey Sharp <jamey@minilop.net>
Cc: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Keith Packard <keithp@keithp.com>