Fix reading from a large compressed file using external process

Previously, only the uncompressed data was "large", but issue #160 is only triggered if the *compressed* data is large (in this case, larger than 128 kB), which apparently exceeds some input buffer. ~~This only ensures the tests are failing, no fix yet.~~ This includes an attempt at a fix where the process is first terminated and *then* the reader thread is told to stop. See #160