Fix bug in MergeSamFiles with USE_THREADING=true.  Sometimes not all the records would get to the output.
Fix bug in MergeSamFiles with USE_THREADING=true.  Sometimes not all the records would get to the output.

broadinstitute/picard,broadinstitute/picard,annkupi/picard,annkupi/picard,alecw/picard,broadinstitute/picard,alecw/picard,broadinstitute/picard,alecw/picard,nh13/picard,nh13/picard,annkupi/picard,alecw/picard,nh13/picard,broadinstitute/picard,annkupi/picard,nh13/picard