Return NO_MEMORY when glReadPixels() fails.

Change-Id: Ic66134ef457e8442ae9135e9ec50e3d02932a253
diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index 8fa0800..a0d2827 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -2815,6 +2815,8 @@
                     *h = sh;
                     *f = PIXEL_FORMAT_RGBA_8888;
                     result = NO_ERROR;
+                } else {
+                    result = NO_MEMORY;
                 }
             } else {
                 result = NO_MEMORY;