Add quotes to multiword arguments.

This adds quotes around multiword arguments before they are passed to
`/bin/sh -c` in an exec command.

Example:

I connect to irc like this:

    exec termite -e "mosh server tmux a"

Without this patch the arguments are passed to sh as:

    termite -e mosh server tmux a

When it should be:

    termite -e "mosh server tmux a"

For the command to work.

sway/commands.c

@@ -361,8 +361,10 @@ static struct cmd_results *cmd_exec_always(int argc, char **argv) {
 			return error;
 		}
 
+		add_quotes(argv + 1, argc - 1);
 		tmp = join_args(argv + 1, argc - 1);
 	} else {
+		add_quotes(argv, argc);
 		tmp = join_args(argv, argc);
 	}