banlist: update set dirty to be more fine grained

- move the SetBannedSetDirty(false) call from DumpData() into DumpBanlist()
- ensure we only set false, if the write succeeded

src/net.cpp

@@ -1455,10 +1455,7 @@ void DumpData()
     DumpAddresses();
 
     if (CNode::BannedSetIsDirty())
-    {
         DumpBanlist();
-        CNode::SetBannedSetDirty(false);
-    }
 }
 
 void static ProcessOneShot()
@@ -2484,14 +2481,14 @@ bool CBanDB::Read(banmap_t& banSet)
 void DumpBanlist()
 {
     int64_t nStart = GetTimeMillis();
-
+    CNode::SweepBanned(); // clean unused entries (if bantime has expired)
-    CNode::SweepBanned(); //clean unused entries (if bantime has expired)
 
     CBanDB bandb;
     banmap_t banmap;
     CNode::GetBanned(banmap);
-    bandb.Write(banmap);
+    if (bandb.Write(banmap))
+        CNode::SetBannedSetDirty(false);
 
     LogPrint("net", "Flushed %d banned node ips/subnets to banlist.dat  %dms\n",
-             banmap.size(), GetTimeMillis() - nStart);
+        banmap.size(), GetTimeMillis() - nStart);
 }