Convolution Reverb: no way to relocate missing IR

Hi there,

I don't think this behavior is specific to the Convolution Reverb device, but here is the repro:

1. Load up a custom IR in the Convolution Reverb from disk

2. Save the project and close it

3. Move or delete the IR file from disk

4. Reopen the project

5. Observe that the device is now suddenly using a default IR

In my opinion, this is a major issue. This means that if the path of an IR file changes, a project using it may suddenly sound completely different, and the user won't be able to tell why. This happened to me when changing PC and I can no longer make some old projects sound like the released version as I don't remember which IRs from my huge library were used.

I believe Ableton should be able to report it like any other missing audio assets.