util/jsoncomm: chain the BufferError in recv

Explicit re-raise the BufferError exception in recv from the orignal
JSONDecodeError, so the latter gets recorded as the underlying cause.

Uncovered by pylint 2.6.0: W0707: "Not using raise from makes the
traceback inaccurate, because the message implies there is a bug in
the exception-handling code itself, which is a separate situation
than wrapping an exception."

osbuild/util/jsoncomm.py

@@ -316,8 +316,8 @@ class Socket(contextlib.AbstractContextManager):
 
         try:
             payload = json.loads(msg[0])
-        except json.JSONDecodeError:
-            raise BufferError
+        except json.JSONDecodeError as e:
+            raise BufferError from e
 
         return (payload, fdset, msg[3])