minor fixes to async logging
minor fixes to async logging

hellowshinobu/easyloggingpp,spthaolt/easyloggingpp,lisong521/easyloggingpp,dreal-deps/easyloggingpp,arvidsson/easyloggingpp,utiasASRL/easyloggingpp,hellowshinobu/easyloggingpp,simonhang/easyloggingpp,spqr33/easyloggingpp,lisong521/easyloggingpp,dreal-deps/easyloggingpp,spthaolt/easyloggingpp,chenmusun/easyloggingpp,arvidsson/easyloggingpp,arvidsson/easyloggingpp,chenmusun/easyloggingpp,utiasASRL/easyloggingpp,spthaolt/easyloggingpp,lisong521/easyloggingpp,blankme/easyloggingpp,simonhang/easyloggingpp,dreal-deps/easyloggingpp,spqr33/easyloggingpp,utiasASRL/easyloggingpp,chenmusun/easyloggingpp,spqr33/easyloggingpp,simonhang/easyloggingpp,hellowshinobu/easyloggingpp,blankme/easyloggingpp,blankme/easyloggingpp