Multi-threading bug fix:

Error in bam_uncompress_input and its use of non-blocking mode. It had
the conditional back to front, so could still deadlock in rare cases
(as well as unnecessarily waiting in others, harming performance).


git-svn-id: svn://svn.code.sf.net/p/staden/code/io_lib@3601 ba6f2710-ca9f-427c-89d3-5bf716dbc8e1