Early out the texture key generation if there is no texture passed to the GrGLShaderBuilder::keyForTextureAccess.  

Under normal circumstances, there will always be a passed texture.  However, when running in the unit tests, CustomStages are constructed without a texture input.
Review URL: https://codereview.appspot.com/6450083

git-svn-id: http://skia.googlecode.com/svn/trunk@4924 2bbb7eff-a529-9590-31e7-b0007b416f81
1 file changed