Fix flashing wifi dialog after rotating back from landscape.

There was an error in some of the OpenGL layer logic such that we would
occasionally set up a layer for rendering and then not clean up when it was
done. This caused future OpenGL rendering to go into that layer instead of
to the buffers being displayed on the screen, resulting in artifacts including
flashes and displaying of stale content. This happened specifically when
using the wifi settings dialog with the InputMethod keyboard displayed,
but it was probably visible in other situations as well.

Issue #5628248: Flickering/flashing after entering password for WiFi

Change-Id: I38139f620b310f4309570fa7224552d2ee633999