Remove weird and buggy try/except block

This is really weird code. I don't know how it has gone unnoticed for so long.

First of all, nothing in that try block could raise `DoesNotExist`. Passing an empty `QuerySet` to `list` returns an empty list with no error. The except block I removed was never being executed. This code only happens to work and appropriately raise `IndexError` because directly indexing the empty list raises the correct error itself.

But the except code itself is bad. `e.args` is a tuple, so passing it as the first argument to `IndexError` casts it as a string and uses it as the message:

    IndexError: ('list index out of range',)

What was meant was probably to to pass either `*e.args` or simply `e.message`.

Briefly exploring the commit history, the code seems to have been like this for a long, long time.

I *could* change the code so that the message of the `IndexError` is the same as the `DoesNotExist` exception like so:

    IndexError: <model name> matching query does not exist.

As that seems to be what was originally intended. I won't make that decision myself though.

For now, the functionality is unchanged but the code itself is simplified with these nonsensical parts removed.