[media] Error 404 is shown when media module trays to instantiate a non existing instrument.

[racostas]

Describe the bug
The media module try to instantiate the instruments that "were associated" to the media file as a sanity check.
This a very good practice.
The issue arrives when for some reason the one of the instruments could not be instantiated. In this case the module will not load and display a 404 error instead.

To Reproduce
Steps to reproduce the behavior (attach screenshots if applicable):

1. Pre-requisite: Having a least one instrument associated to a media file that could not be instantiated by LORIS for one reason or other (eg, the name of the instrument was changed and not updated in the media module, the instrument was deleted, etc.)
2. Go to MainMenu->Clinical->Media
3. The module will not load. And a 404 error will be shown in place.
4. No trace will is left in the error-log file neither.

What did you expect to happen?
The module to load and to log the specific issue with the instrument in the log file.

Additional context
This issue could appear if the name of an instrument is changed, the instrument is deleted, etc. and not properly updated in the media module linked file. The proposal is not to break the module for this reason but to let it load and log the issue with the particular instrument in the error-log instead.