hg: openjfx/8/graphics/rt: RT-33562: Java_com_sun_prism_es2_GLContext_nReadPixelsByte/Int need to check null pointer

[hang.vo at oracle.com]

Changeset: 38e7cca64cd7
Author:    Yao Wang <yao.w.wang at oracle.com>
Date:      2013-10-15 14:28 -0700
URL:       http://hg.openjdk.java.net/openjfx/8/graphics/rt/rev/38e7cca64cd7

RT-33562: Java_com_sun_prism_es2_GLContext_nReadPixelsByte/Int need to check null pointer
Reviewed-by: kcr, cyang

! modules/graphics/src/main/native-prism-es2/GLContext.c