[Bug report] Constantly using "Clone Steps" on a Pattern clip causes LMMS to freeze

Steps to reproduce:
1. Make a BB clip
2. It should have at least one cell playing something
3. Spam "Clone Steps"
4. LMMS will take longer to clone the data with each consequent "Clone Steps" click
5. Eventually, it'll freeze entirely

@Monospace-V claims this doesn't happen on 1.2.

Start by reproducing the freeze in LMMS with a BB clip containing a playing cell, then repeatedly use "Clone Steps" while observing the increasing delay. Compare the behavior with version 1.2; done means repeated cloning no longer progressively slows LMMS or freezes it.

Written by the indexing model from the issue text.