The text a user types to set the channel index should clear itself when the targeted pattern changes

[ThinkAndWander]

If the playhead moves, the target pattern that would be set by typing numbers necessarily also changes. However, the current typed value stored behind-the-scenes does not clear.

i.e. you can type the number "1", then go to the next channel and type "1" and it will set it to "11" (if you have that many channel indices) even though the target channel has changed.

Repro:

1. Create a new project
2. Set the first pattern's index to 2

4. In Channel Settings... set 11 or more allowed (so you can type "11")

6. Press space to start playback and press 1 as it plays the first pattern
7. While playback continues, press 1 as it goes through the second index

Expected result - it sets the second index to "1" Actual result - it sets the second index to "11"