Revert "Do not always check if __main__ in result when pickling (da…

…sk#8443)"

This reverts commit 5c481dd.

distributed/protocol/pickle.py

@@ -67,19 +67,14 @@ def dumps(x, *, buffer_callback=None, protocol=HIGHEST_PROTOCOL):
             buffers.clear()
             pickler.dump(x)
             result = f.getvalue()
-
-        if not _always_use_pickle_for(x) and (
+        if b"__main__" in result or (
             CLOUDPICKLE_GE_20
             and getattr(inspect.getmodule(x), "__name__", None)
             in cloudpickle.list_registry_pickle_by_value()
-            or (
-                len(result) < 1000
-                # Do this very last since it's expensive
-                and b"__main__" in result
-            )
         ):
-            buffers.clear()
-            result = cloudpickle.dumps(x, **dump_kwargs)
+            if len(result) < 1000 or not _always_use_pickle_for(x):
+                buffers.clear()
+                result = cloudpickle.dumps(x, **dump_kwargs)
     except Exception:
         try:
             buffers.clear()