bubblewrap: Adjust wording in a comment

Adjust wording in one of the comment, to read more clearly.

Consider the previous wording:

"... a problem if we're privileged, if we're not opt_unshare_user ..."

it might sound like the "not" refers to `opt_unshare_user`, while in
fact refers to "being privileged" from the previous sentence.

Adding a "then" removes the ambiguity, making the message flow better,
especially for non-native English readers.

Signed-off-by: Antonio Ospite <antonio.ospite@collabora.com>

Author: ao2

bubblewrap.c

@@ -2674,8 +2674,8 @@ main (int    argc,
         }
 
       /* Debian lets you disable *unprivileged* user namespaces. However this is not
-         a problem if we're privileged, and if we're not opt_unshare_user is true
-         already, and there is not much we can do, its just a non-working setup. */
+         a problem if we're privileged, and if we're not then opt_unshare_user is true
+         already, and there is not much we can do, it's just a non-working setup. */
 
       if (!disabled)
         opt_unshare_user = true;