Related with issue #6113.
`(old_buf_size & 0xC0000000) != 0` checks if we can duplicate old_buf_size
and still be under 2GB (by checking if bit 30 or 31 is 1). This doesn't
allow buffers larger than 1GB.
The strategy now is to allocate a buffer with the maximum array size
when we detect that we are overflowing the 2GB.
Also changed default buffer size to 1024.
f96d1ef744