egl: handle failed eglMakeCurrent EGL_NO_CONTEXT

The recovery code for failed eglMakeCurrent didn't correctly
handle the case when the previous context was EGL_NO_CONTEXT.
Leave the original EGL context unrestored in that case.
The driver should be able to handle that case without help.

Bug: 38341617, 37244059
Change-Id: I38f3450005a4eec5f1a684ee7d66363e88f6d92f
Fixes: 38341617
Test: android.server.cts.ActivityManagerDisplayTests, Run Minions Rush app.