ES: Replace useless asserts with proper checks

It makes absolutely no sense to have asserts for what is obviously an
error condition. And they should definitely not cause Dolphin to crash
because it assumes that everything is valid, and Dolphin should not
report those to the user either, as it is very obviously a bug in the
emulated software and there is nothing the user (or we) can do.

This commit replaces all of the request asserts with proper checks
and adds missing checks for some ioctlvs. We still do not check sizes
yet; this will be done later.