ANGLE: Reorder debug package check

As originally coded, debug ANGLE packages could only be used
if ANGLE was properly installed, such that a single answer
was received from ANGLE_FOR_ANDROID.  Since ANGLE is only
required on new Q devices, debug packages could not be loaded
on devices that upgraded from P.

This CL changes the ordering such that debug packages are
detected before checking for propertly installed ANGLE package.

Bug: 132076614
Test: Manually test app with and without debug package
Test: atest CtsAngleIntegrationHostTestCases

Change-Id: I88f0417c7e74c2c20d087f2137eeb78879143ce5