Fix stack overflow in rpm2extents
    
    Creation of array struct digestoffset offsets[rpmfiFC(fi)] caused a
    stack overflow because the total size is greater than 8M which is the
    stack size limit on Linux. To fix the issue, the array is allocated on
    the heap.
    
    I used AddressSanitizer to find the root cause of the issue. It found a
    number of memory leaks so I fixed them as well.