Vulkan: Bugfix in resolvePrecisionMismatch(...) Early-return if a varying is not active in either the front or back shader Bug: angleproject:386749841 Test: GLSLTest.MismatchedInactiveVarying* Change-Id: Ie0c6dfd6616afcb94bec043d36d4f8188df8abb3 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6239031 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: mohan maiya <m.maiya@samsung.com>