Fix a memory corruption issue when vector resize

There is memory corruption in below code

const Rect* prev = &dst[prevIndex];
dst.add(Rect(prev->right, top, right, bottom));

prev points to a memory of vector dst, when dst resize in add()
call, the memory that prev points to will be copy to the new
allocated vector memory and the old memory will become undefined

Avoid pointer in this case, use a local copy instead

Change-Id: I4d95ceedd00c8fb615ac153082ade1b1ce0d0fa8