Fix #20879: crash when add textures brush in sculpt mode. Drawing

the texture would crash because the VBO was still bound. As I
understand it this is not necessarily against the opengl spec,
but might as well unbind it, the driver bug seems to have been
fixed but has not trickled down everywhere yet.

http://bugs.freedesktop.org/show_bug.cgi?id=23859

source/blender/gpu/intern/gpu_buffers.c

@@ -672,6 +672,9 @@ void GPU_draw_buffers(void *buffers_v)
 			glDrawElements(GL_TRIANGLES, buffers->tot_tri * 3, buffers->index_type, 0);
 		}
 
+		glBindBufferARB(GL_ARRAY_BUFFER_ARB, 0);
+		glBindBufferARB(GL_ELEMENT_ARRAY_BUFFER_ARB, 0);
+
 		glDisableClientState(GL_VERTEX_ARRAY);
 		glDisableClientState(GL_NORMAL_ARRAY);
 	}