memory leak identified in myersCalcEditDistanceSemiGlobal

[GDCCP]

Description

static int myersCalcEditDistanceSemiGlobal(
        const Word* const Peq, const int W, const int maxNumBlocks,
        const int queryLength,
        const unsigned char* const target, const int targetLength,
        int k, const EdlibAlignMode mode,
        int* const bestScore_, int** const positions_, int* const numPositions_) {
    *positions_ = NULL;
    *numPositions_ = 0;

The statement *positinos_ = NULL; can lead to memory leak as *positions_ before the assignment is not released.

This is discovered during code inspection when working on https://github.com/Martinsos/edlib/issues/84