The current implementation throws a segmentation fault when padding
files using a large range, because the writing operation overflows the
source buffer, which was a single char.
IPFS previously assumed that the offset for the seek operation was related
to the start of the file (SEEK_SET). It now correctly checks the parameter
'whence' and computes the offset for SEEK_CUR (middle of the file) and
SEEK_END (end of the file).