JCLOUDS-619

Hello,

this is the fix for the issue described here[1].

Please review and let me know if you need something else.

Thanks and kind regards
Markus

[1] https://issues.apache.org/jira/browse/JCLOUDS-619
All of this code will go away with the suggested `ByteSource` changes, but note that this code is wildly inefficient, requiring one system call per byte.