prepare-commit-msg should be no-op with --no-edit

https://bugs.webkit.org/show_bug.cgi?id=240689

Reviewed by Jonathan Bedard.

* Tools/Scripts/hooks/prepare-commit-msg:

Canonical link: https://commits.webkit.org/250779@main
git-svn-id: https://svn.webkit.org/repository/webkit/trunk@294524 268f45cc-cd09-0410-ab3c-d52691b4dbfc

Tools/Scripts/hooks/prepare-commit-msg

@@ -77,6 +77,10 @@ def main(file_name=None, source=None, sha=None):
     if source not in (None, 'commit', 'template'):
         return 0
 
+    if os.environ.get('GIT_EDITOR', '') == ':':
+        # When there's no editor being launched, do nothing.
+        return 0
+
     with open(file_name, 'w') as commit_message_file:
         if sha:
             commit_message_file.write(subprocess.check_output(