Correctly test for a null pointer before going and dereferencing it.

This defect was found automatically by Coverity Prevent, a static analysis
tool.
Signed-off-by: Zaur Kambarov <zkambarov@coverity.com>
Cc: <linux-fbdev-devel@lists.sourceforge.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>