Fix no attachment framebuffer validations

A framebuffer without an attachment can be complete if it has a nonzero
default width and height. Moreover these parameters can be reset to zero
later, invalidating the framebuffer's completeness status. These changes
update the guest to properly handle both scenarios.

Bug: 172281537
Test: Ran GLES 3.1 DEQP tests.
Change-Id: Iad26469df00b53f079d9050c3f577edc4c83fb38
4 files changed