symbols: Fix inconsistent error handling Currently the following keymap triggers a critical error (invalid `vmods`) only for the second key statement, while it should handle both equally. ``` xkb_keymap { xkb_keycodes { <> = 9; }; xkb_types { }; xkb_compat { }; xkb_symbols { key <> { vmods = [], repeats = false }; key <> { repeats = false, vmods = [] }; }; }; ``` Fixed by parsing the whole symbols body and failing if any error was found.