file-remote-p should not return user-error on some strings

[Thierry Volpiatto]

Hi Michael,

I have a bug report at helm about an error when calling helm-find-files
on a string like address@hidden://www.doc.ic.ac.uk/lab/cplus/c++.rules/}`.
Seeing the backtrace, it looks it comes from `file-remote-p` which
return a user-error in such case, perhaps it should return nil ?

See https://github.com/emacs-helm/helm/issues/1638

Note that this is not reproductible on emacs-24.5.

Thanks.