Use-after-free of a dictionary after a one-shot call on a context with an open stream

The one-shot `DCtx` and `CCtx` methods assumed the C library resets the
context, but it leaves an open stream as it is. When a stream was left
unfinished on a context, a one-shot call such as `decompress_using_dict`
could leave the context pointing at the dictionary borrowed for that call,
and the next streaming call resumed the stream against it after it was
freed: decompressed output then contained freed heap memory. On the
compression side, the stream resumed against the one-shot call's buffers.

This requires an application to use one context for both streaming and
one-shot calls without a reset in between. The flaw was corrected by
resetting the session after one-shot calls whenever a stream may be open.