privval: avoid re-signing vote when RHS and signbytes are equal (#7592)

* avoid re-signing vote when RHS and signbytes are equal

* avoid re-signing proposal when RHS and signbytes are equal

Co-authored-by: Callum Waters <cmwaters19@gmail.com>
Co-authored-by: William Banfield <4561443+williambanfield@users.noreply.github.com>

privval/file.go

@@ -371,8 +371,8 @@ func (pv *FilePV) signVote(chainID string, vote *tmproto.Vote) error {
 
 			vote.Timestamp = timestamp
 			vote.Signature = lss.Signature
-			return nil
 		}
+		return nil
 	}
 
 	// It passed the checks. Sign the vote