cli: option autocompletion should not match words without trailing '-'

This would fix for example:
nmcli e <TAB>
(e interpreted as --escape, would allow autocompletion to work... but
when the command is executed an error is reported)

Moreover, we will now have:
nmcli c <TAB>
autocompletion work correctly, i.e., c is correctly interpreted  as
"connection" instead of "--colors"

clients/cli/nmcli-completion

@@ -123,6 +123,8 @@ _nmcli_compl_match_option()
         S="${S:2}"
     elif [[ "${S:0:1}" == "-" ]]; then
         S="${S:1}"
+    else
+        return 1
     fi
     for V; do
         case "$V" in