[Bugfix] row hash tries to match position 0 (#3548)

[Bugfix] row hash tries to match position 0 (#3548)

#3543 decreases the size of the tagTable by a factor of 2, which requires using the first tag position in each row for head position instead of a tag.
Although position 0 stopped being a valid match, it still persisted in mask calculation resulting in the matches loops possibly terminating before it should have. The fix skips position 0 to solve this problem.