modifiers request by the input method is supposed to send the raw
modifiers based on the keymap of the keyboard grabbed as result of the
grab_keyboard request. If input method client is not using the keysym
functionality it can decide to not send out the modifiers_map, since it
is already known to compositor as part of keymap event sent by it.

While at it also guard against empty modifiers_map, if this happens
ideally compositor should handle that information based on the keymap
sent out using grab_keyboard function, but since currently, we do not
have the grab_keyboard implemented in here, send out the NoModifier if
that happens.