find_region_range in mm.c is skipping regions by using RB_LEFT 

Im getting overlapping regions errors with the original code as it 
seems to skip sections when doing munmap.
find_region_range should iterate the tree by using RB_PREV or by going down the tree as below.

for (struct mm_region *r = leftmost;NULL != r;){
    if (region_compare(&find, r) == 0){
      leftmost = r;
      r = RB_LEFT(r, tree);
    } else
      r = RB_RIGHT(r, tree);
  }