HoughLinesSDiv use this pivot to get line whose accumalor value is greater than threshold, and it has been kept at the end in the vector lst.

So when create outputarray, in this scenario, lines, whose height is equal to the size of the lst, but skip over the initialization of the last element of lines , leaving the value undefined.

Actually, the pivot is always at the end of the vector lst. It would be reasonable to solve this problem by creating lines with the height equal to lst.size()-1.