Fix edge case where TDPuller never stops if told to stop before it catches up
Fix edge case where TDPuller never stops if told to stop before it catches up

This in turn was resulting in the puller never re-starting after the app was reactivated.
Fixes #169 (I hope)

evsukov89/couchbase-lite-ios,macoscope/couchbase-lite-ios,pellekrogholt/couchbase-lite-ios,alfared/couchbase-lite-ios,evsukov89/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,alfared/couchbase-lite-ios,couchbase/couchbase-lite-ios,ryuzmukhametov/couchbase-lite-ios,brendand/couchbase-lite-ios,evsukov89/couchbase-lite-ios,amco/couchbase-lite-ios,pegli/couchbase-lite-ios,myDario/couchbase-lite-ios,couchbase/couchbase-lite-ios,amco/couchbase-lite-ios,Chavenay/couchbase-lite-ios,amco/couchbase-lite-ios,alfared/couchbase-lite-ios,mz2/couchbase-lite-ios,pellekrogholt/couchbase-lite-ios,pellekrogholt/couchbase-lite-ios,brendand/couchbase-lite-ios,gotmyjobs/couchbase-lite-ios,tomco/couchbase-lite-ios,jkingyens/couchbase-lite-ios,myDario/couchbase-lite-ios,mz2/couchbase-lite-ios,pegli/couchbase-lite-ios,lordkev/couchbase-lite-ios,ipmobiletech/couchbase-lite-ios,myDario/couchbase-lite-ios,jkingyens/couchbase-lite-ios,brendand/couchbase-lite-ios,gotmyjobs/couchbase-lite-ios,macoscope/couchbase-lite-ios,pegli/couchbase-lite-ios,brendand/couchbase-lite-ios,amco/couchbase-lite-ios,macoscope/couchbase-lite-ios,pellekrogholt/couchbase-lite-ios,ipmobiletech/couchbase-lite-ios,gotmyjobs/couchbase-lite-ios,ipmobiletech/couchbase-lite-ios,couchbase/couchbase-lite-ios,macoscope/couchbase-lite-ios,ryuzmukhametov/couchbase-lite-ios,alfared/couchbase-lite-ios,amco/couchbase-lite-ios,tomco/couchbase-lite-ios,pegli/couchbase-lite-ios,amco/couchbase-lite-ios,amco/couchbase-lite-ios,tomco/couchbase-lite-ios,ryuzmukhametov/couchbase-lite-ios,ryuzmukhametov/couchbase-lite-ios,tomco/couchbase-lite-ios,jkingyens/couchbase-lite-ios,ipmobiletech/couchbase-lite-ios,gotmyjobs/couchbase-lite-ios,couchbase/couchbase-lite-ios,lordkev/couchbase-lite-ios,brendand/couchbase-lite-ios,Chavenay/couchbase-lite-ios,lordkev/couchbase-lite-ios,jkingyens/couchbase-lite-ios,mz2/couchbase-lite-ios,lordkev/couchbase-lite-ios,Chavenay/couchbase-lite-ios