fix bitmap shader leak in gm

this was introduced in https://codereview.chromium.org/245963010

this was detected by caryclark@ by examining the result of valgrind on the skia buildbots

BUG=skia:1976
R=caryclark@google.com

Author: dominikg@chromium.org

Review URL: https://codereview.chromium.org/255253002

git-svn-id: http://skia.googlecode.com/svn/trunk@14450 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed