Fixed error reporting

[RunDevelopment]

This fixes 2 bugs:

1. The frontend assumes that all inputs have information about their current values. This is not the case. If the logic for deriving this information fails, we don't have it. If the node executor itself has a bug, we don't have this information either. Since error reporting must not fail, I choose to conservatively assume that we might not have values for everything.
2. get_error_value was implemented incorrectly for ImageInput. The value could be None, but this was not accounted for. This is the 'NoneType' object has no attribute 'shape' we see here.

In addition to this, I also added a try around collection error data. It's better to have less data than for the collection itself to error and hide the original error.

Error reporting should now be a lot more robust.