Don't do remote checks on NULL files

Don't do remote checks on NULL files

Calling _gtk_file_consider_as_remote() with a NULL argument
results in warnings being thrown.

Note that query->priv->location being NULL is a state that does
not seem to be invalid by itself.

This could happen if you do search-as-you-type in a filechooser,
which has a filter that does not match anything *and* the current
"place" selected is "Recent".

https://bugzilla.gnome.org/show_bug.cgi?id=761552