[1578] fixed typo in comment

src/lib/datasrc/memory_datasrc.cc

@@ -629,7 +629,7 @@ struct InMemoryZoneFinder::InMemoryZoneFinderImpl {
     // Set up FindResult object as a return value of find(), taking into
     // account wildcard matches and DNSSEC information.  We set the NSEC/NSEC3
     // flag when applicable regardless of the find option; the caller would
-    // simply ignore these when then didn't request DNSSEC related results.
+    // simply ignore these when they didn't request DNSSEC related results.
     FindResult createFindResult(Result code, ConstRRsetPtr rrset,
                                 bool wild) const
     {