Fix AbstractDiskHttpData int conversion from long

Motivations:
The chunkSize might be oversized after comparison (size being > of int capacity) if file size is bigger than an integer.

Modifications:
Removing the test and changing of chunkSize value, letting it be standard at 8K.

Result:
There is no need to change the chunksize as it has not to be less or equal to the number of bytes available.
There is no more int oversized.