Fix OpenXR for Official Builds

It seems as though Java asserts are stripped out on official builds.
This change thus moves a call that was happening inside of an assert
(which had the side effect of continuing the requestSession call) to
outside of it, while still asserting on the result returned from it.
This unblocks launching an OpenXR session on official builds on
Android.

Fixed: 1521427
Change-Id: Ic53170810e3ac81990101654704646f19c4e7c9e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5235006
Auto-Submit: Alexander Cooper <alcooper@chromium.org>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Commit-Queue: Brandon Jones <bajones@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1251725}