examples/gl_basic: use glReadPixels to verify correct drawing
examples/gl_basic: use glReadPixels to verify correct drawing

Signed-off-by: Jordan Justen <a79006884ba9cf5f4f7fcbb92a15b208780d8c97@intel.com>
(chad): Fix 3-space indent to 4-space.
Signed-off-by: Chad Versace <a557f7f75bf28dc19ac99107f5cc7cd6b3fbdb1a@linux.intel.com>

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