Fix flag for checking if a row-length specialised implementation has been used so that it is reset each row.
Fix flag for checking if a row-length specialised implementation has been used
so that it is reset each row.

Monotone-Parent: 2a2caca203bc82fc55fb5f9ee2058f3942b9b33f
Monotone-Revision: 5c3b50e364b25356ac0a0fb07d97957575c59df5

FrancisRussell/desola,FrancisRussell/desola,FrancisRussell/desola