better flow for bootsrap ci download process

src/bootstrap/bootstrap.py

@@ -1156,25 +1156,21 @@ def bootstrap(args):
 
     try:
         last_commit = build.last_bootstrap_commit()
-        if not bootstrap_bin.exists and not build.bootstrap_out_of_date(last_commit):
-            success = build.download_bootstrap(last_commit)
-
-            if success:
-                stamp = pathlib.Path(build.build_dir).joinpath("bootstrap/.bootstrap-stamp")
-                stamp.write_text(last_commit)
-                build.is_precompiled_bootstrap = True
-
-        else:
+        if last_commit is None:
             build.build_bootstrap()
+        else:
+            if build.bootstrap_out_of_date(last_commit):
+                success = build.download_bootstrap(last_commit)
+                if success:
+                    stamp = pathlib.Path(build.build_dir).joinpath("bootstrap/.bootstrap-stamp")
+                    stamp.write_text(last_commit)
+                    build.is_precompiled_bootstrap = True
+                else:
+                    build.build_bootstrap()
 
     except Exception as e:
-        import traceback
-        print(traceback.format_exc())
         print(str(e))
 
-    if not build.is_precompiled_bootstrap:
-        build.build_bootstrap()
-
 
     sys.stdout.flush()