Output user-defines start label in the appropriate place.

Output user-defines start label in the appropriate place.

Before this commit, given the following example:
    /*!re2c
            re2c:startlabel = "start";
            [^]* {}
    */
re2c would generate the following code:
    {
            YYCTYPE yych;
            goto yy0;
    yy1:
    start:
            ++YYCURSOR;
    yy0:
            if (YYLIMIT <= YYCURSOR) YYFILL(1);
            yych = *YYCURSOR;
            goto yy1;
            {}
    }
where "start:" falsely corresponds to "yy1:" rather to "yy0:".
(The important property of this example is that DFA has arrows
to initial state.) This commit fixes this behavior:
    {
            YYCTYPE yych;
    start:
            goto yy0;
    yy1:
            ++YYCURSOR;
    yy0:
            if (YYLIMIT <= YYCURSOR) YYFILL(1);
            yych = *YYCURSOR;
            goto yy1;
            {}
    }