Find the memory blocks that span size bytes starting from offset
in buffer.
When this function returns TRUE, idx will contain the index of the first
memory bock where the byte for offset can be found and length contains the
number of memory blocks containing the size remaining bytes. skip contains
the number of bytes to skip in the memory bock at idx to get to the byte
for offset.
size can be -1 to get all the memory blocks after idx.
Find the memory blocks that span size bytes starting from offset in buffer. When this function returns TRUE, idx will contain the index of the first memory bock where the byte for offset can be found and length contains the number of memory blocks containing the size remaining bytes. skip contains the number of bytes to skip in the memory bock at idx to get to the byte for offset. size can be -1 to get all the memory blocks after idx.