Show full PKGBUILD if a commit id is not found

If a git commit id is not found in a PKGBUILD repository, show the full
PKGBUILD instead of trying to show a git diff.

Fixes #5

example/source.py

@@ -230,6 +230,9 @@ class MyCommands(decman.config.Commands):
     def git_get_commit_id(self) -> list[str]:
         return ["git", "rev-parse", "HEAD"]
 
+    def git_log_commit_ids(self) -> list[str]:
+        return ["git", "log", "--format=format:%H"]
+
     def review_file(self, file: str) -> list[str]:
         return ["less", file]