Problem:    Tests fail because some changes were not included.
Solution:   Add changes to evalfunc.c
https://github.com/vim/vim/commit/3a29abcb6154d9f55ca8abd6d97e5822b97ac4b3

- Return VimL errors instead of generic errors for:
  - nvim_call_function
  - nvim_call_dict_function
- Fix tests which were silently broken before this change.

This violates #6150 where we agreed not to translate API errors.  But
that can be fixed later.

closes #4983

I failed to deduce why analyzer thinks E882 may not be triggered, though 
conditions for triggering it are strange: it would trigger E882 only in the 
single case “function returned non-number”. Cases “function thrown exception”, 
or “built-in sorter encountered error” will neither yield E882 nor stop 
sort()/uniq().

Note though that searching test code revealed that neither E702 nor E882 are not 
tested anywhere.

Before this change, if $NVIM_LISTEN_ADDRESS was invalid, v:servername
was left empty.