Fix `egl_debug_log`
Fix `egl_debug_log`

https://registry.khronos.org/EGL/extensions/KHR/EGL_KHR_debug.txt

As defined by the spec, `message` can be `NULL`, so this needs to handle
that possibility.

The first argument is not "severity", it is an error code. The severity
is instead the third argument, `messageType`.

Since message can be null, converting the error code to a string can be
necessary to actually convey useful information.

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