Sample TCO length not responsive to BPM

To reproduce: Load a sample in a sample track, then drag on the BPM display to change BPM.

[Here's a video.](https://www.youtube.com/watch?v=lih9E0VP1Uo) First I try to "refresh" the clip by dragging it and zooming, then I try cloning it. After that I reload the sample by double clicking and selecting the same file, which does nothing. Finally, deleting and reloading the sample from scratch sets it to the new BPM, but it exhibits the same behavior after that.

Tested in 64bit RC5 on Windows 10.

Start by reproducing the issue in a sample track: load a sample, change the BPM from the BPM display, and observe whether the sample's length changes. Check the sample-track handling of BPM changes and compare it with deleting and reloading the sample; done means the existing sample responds to BPM changes without requiring a reload.

Written by the indexing model from the issue text.