Steps to reproduce

Related to #5054
Start a Chinese IME composition without completing it/selecting the characters e.g. "wei'yuan", then delete the characters.

Expected behavior

There should be no characters left on the screen.

Actual behavior

The letter "w" will appear in the buffer.

Cause

We're receiving a CompositionCompleted event before we receive a TextUpdating event for the final character "w" to be deleted. This causes us to believe that "w" is a completed composition, so we send it to the terminal. We then receive the TextUpdating event right after to tell us to delete the "w", so it disappears from the _inputBuffer.