egl: Emit error when eglGetDisplay or eglIntialize fails

When these EGL functions failed, waffle_display_connect() returned false
but waffle_error_get_code() returned WAFFLE_NO_ERROR. This patch emits
WAFFLE_ERROR_UNKNOWN through wegl_emit_error().

For-Stable: Candidate for 1.2.
Signed-off-by: Chad Versace <chad.versace@linux.intel.com>