fixed a long-standing bug on #LNTYPE 2 handling.

reported by Hitkey through his blog:
http://hitkey.nekokan.dyndns.info/diary1406.php#D140620

this is a worrisome bug showing the needs for proper test cases (ugh).
specifically, any BMS file with more than two LNs in the same lane
would parse incorrectly due to the failure to clear the initial LN.
this bug was introduced by a488d81d35e8447d604d35d8490ab1af6f9625f6.