Wrap get_gitHash in try-catch to prevent failures in tarball builds.

Bug: chromium:1321370
Change-Id: If39d2236d1b4d965f7bd189f6bd1cdc70436c41d
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/88582
Commit-Queue: Loko Kung <lokokung@google.com>
Reviewed-by: Austin Eng <enga@chromium.org>
Kokoro: Kokoro <noreply+kokoro@google.com>

generator/dawn_version_generator.py

@@ -27,11 +27,14 @@ def get_git():
 
 
 def get_gitHash(dawnDir):
+    try:
         result = subprocess.run([get_git(), "rev-parse", "HEAD"],
                                 stdout=subprocess.PIPE,
                                 cwd=dawnDir)
         if result.returncode == 0:
             return result.stdout.decode("utf-8").strip()
+    except Exception:
+        return ""
     # No hash was available (possibly) because the directory was not a git checkout. Dawn should
     # explicitly handle its absenece and disable features relying on the hash, i.e. caching.
     return ""