bug#50340: Fix remote-location in vc-git-log-incoming

[Juri Linkov]

>> -  (vc-git-command nil 0 nil "fetch")
>> +  (vc-git-command nil 0 nil "fetch" (unless (string= remote-location "")
>> +                                      remote-location))
>
> I'm not sure which scenario this fixes (pressing RET after 'C-u C-x v I'
> works fine here), but it shouldn't hurt either.

It fixes the scenario with a non-default remote.  Could you try 'C-u C-x v I'
and typing the name of a non-default remote in a repo with two remotes?
I wonder if it already worked, and maybe I have some misconfiguration.

> So if you have a stable repro (some alternative completing-read-function?),
> you can go ahead and install.

Regarding the default completing-read-function, the prompt of 'C-u C-x v I'
doesn't provide completion on remote names.  Maybe this should be improved
as well.