Add checks for invalid cases “a[]” and "a[a]" in array parsing Returns empty outSubscripts vector for a[] Adds GL_INVALID_INDEX to outSubscripts for a[a] Bug: angleproject:401979815 Change-Id: Ie18e9bbbec2b15cac69ae048b81f14ab13439400 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6339329 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Auto-Submit: Mavis Deng <mavis.deng@arm.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>