small fix

Author: funbringer

testgres/testgres.py

@@ -868,8 +868,7 @@ def safe_psql(self, dbname, query, username=None):
 
         ret, out, err = self.psql(dbname, query, username=username)
         if ret:
-            if err:
-                err = err.decode('utf-8')
+            err = '' if not err else err.decode('utf-8')
             raise QueryException(err)
         return out