fix(utils): filter_symbols return table consistently (#3421)

Previously, filter_symbols returned nil in certain cases, which could
lead to unexpected behavior. This change ensures that an empty table is
always returned, maintaining consistency.

lua/telescope/utils.lua

@@ -180,6 +180,7 @@ utils.filter_symbols = function(results, opts, post_filter)
       level = "WARN",
     })
   end
+  return {}
 end
 
 local path_filename_first = function(path, reverse_directories)