egl/dri2: check if the EGL API is valid before adding it to ClientAPIs

egl/dri2: check if the EGL API is valid before adding it to ClientAPIs

In the rather unlikely case that the API is considered invalid, don't
add it to the (supported) ClientAPIs bitmask.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
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Strictly speaking we only need this in the Android case for OpenGL.
Adding it everywhere doesn't hurt us since the compiler will const
propagate and optimise/remove these.