cli,output: fix truncated array output when == 10 elements

The extra character size was only being applied when > 10 elements,
leaving the == 10 case out of it, so the output was being truncated.
Fix it, by using a more generic way to computing how many extra
characters we need in the size.

Fixes https://gitlab.freedesktop.org/mobile-broadband/ModemManager/issues/151

cli/mmcli-output.c

@@ -964,8 +964,10 @@ dump_output_keyvalue (void)
 
             n = multiple->values ? g_strv_length (multiple->values) : 0;
             if (n > 0) {
+                guint aux = n;
+
                 key_length += ((strlen (KEY_ARRAY_VALUE_SUFFIX)) + 3);
-                if (n > 10)
+                while ((aux /= 10) > 0)
                     key_length++;
             }
         }