Fix crash on activating a text area without a real keyboard
It will cause on following situation:
- Enable weston-simple-im
- It's also reproducible with IBus or Fcitx5
- Connect a mouse or a touch panel
- Don't connect keyboad
- Launch weston-editor and touch the text area
It doesn't reproduce with weston-keyboard because it doesn't use grab_keyboard of input-method-context-v1.
Signed-off-by: Takuro Ashie ashie@clear-code.com