Translator: Avoid unreachable in presence of shader error When the gl_ClipDistance/gl_CullDistance index is tracked for future validation, the parser expected the index type to be valid, but it may not be if there's a compile error. Bug: angleproject:349994211 Change-Id: I94f39bec34a8ae68ef7d6c3cce256026808c0bc9 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/7042014 Auto-Submit: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Yuxin Hu <yuxinhu@google.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>