Fix: Give better error message for invalid URLs

In some cases a URL can be invalid, i.e. when mistyped an option like `+insecure`.
In this cases `fatal: Remote host not set.` was printed as error message.
Now this message says `... is not a valid host URL.` so the user can see what's wrong.

git-ftp

@@ -616,6 +616,7 @@ set_remote_host() {
  [ -z "$URL" ] && URL="$(get_config url)"
  REMOTE_HOST=$(expr "$URL" : ".*://\([[:alpha:]0-9\.:-]*\).*")
  [ -z "$REMOTE_HOST" ] && REMOTE_HOST=$(expr "$URL" : "\([[:alpha:]0-9\.:-]*\).*")
+ [ -z "$REMOTE_HOST" -a -n "$URL" ] && print_error_and_die "'$URL' is not a valid host URL." "$ERROR_MISSING_ARGUMENTS"
  [ -z "$REMOTE_HOST" ] && print_error_and_die "Remote host not set." "$ERROR_MISSING_ARGUMENTS"
 }