fix crash when validating an invalid EGL objects

the code that validated EGL objects dereferenced the object
to access its EGLDisplay -- needed for validation (!).
This was wrong for two reasons, first we dereferenced the object
before validating it (potentially leading to a crash), secondly
we didn't validate that the object existed in the right EGLDisplay.

We now use the EGLDisplay passed by the user API.

Change-Id: I66f9e851d4f8507892a6b1fee3065f124c4e7138