ASSERT tool.drcacheoff.windows-zlib signal.c:5729 dcontext != GLOBAL_DCONTEXT

This happened once in PR #5506:

http://139.178.82.61:8080/job/DynamoRIO-AArch64-Precommit/1606/consoleFull

232:   *** postcmd failed (255): <Application
232:   /var/lib/jenkins/workspace/DynamoRIO-AArch64-Precommit/build/build_debug-internal-64/clients/bin64/drcachesim
232:   (1817526).  Internal Error: DynamoRIO debug check failure:
232:   /var/lib/jenkins/workspace/DynamoRIO-AArch64-Precommit/core/unix/signal.c:5729
232:   dcontext != GLOBAL_DCONTEXT
232: 
232:   (Error occurred @0 frags in tid 1817612)