fix: make commit grabber use GIT_REV env var if set

Co-authored-by: nekomona <nekomona@163.com>

scripts/get_git_commit.py

@@ -1,19 +1,19 @@
 import subprocess
 import os
 
-revision = "00000000000000000000000000000000000000000"
+revision = ""
 
 env_rev = os.environ.get("GIT_REV")
-if env_rev != "":
+if not env_rev is None and env_rev != "":
     revision = env_rev
-
-try:
-    revision = (
-        subprocess.check_output(["git", "rev-parse", "HEAD"])
-        .strip()
-        .decode("utf-8")
-    )
-except Exception:
-    revision = "NOT_GIT"
+else:
+    try:
+        revision = (
+            subprocess.check_output(["git", "rev-parse", "HEAD"])
+            .strip()
+            .decode("utf-8")
+        )
+    except Exception:
+        revision = "NOT_GIT"
 
 print(f"'-DGIT_REV=\"{revision}\"'")