format: assert that the multi-sample check enters with a clean error state

In order to ensure that all the errors in the initialization are handled
before entering this routine assert on pre-existsing errors.

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Jakob Bornecrantz <jakob@collabora.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/vrend_formats.c

@@ -475,6 +475,9 @@ unsigned vrend_renderer_query_multisample_caps(unsigned max_samples, struct virg
    int out_buf_offsets[4] = {0,1,2,4};
    int lowest_working_ms_count_idx = -1;
 
+   assert(glGetError() == GL_NO_ERROR &&
+          "Stale error state detected, please check for failures in initialization");
+
    glGenFramebuffers( 1, &fbo );
    memset(caps->sample_locations, 0, 8 * sizeof(uint32_t));