Fix de-serialization bug where AddrMan is corrupted after exception

* CAddrDB modified so that when de-serialization code throws an exception Addrman is reset to a clean state
* CAddrDB modified to make unit tests possible
* Regression test created to ensure bug is fixed
* StartNode modifed to clear adrman if CAddrDB::Read returns an error code.

src/net.cpp

@@ -1944,6 +1944,7 @@ void StartNode(boost::thread_group& threadGroup, CScheduler& scheduler)
         if (adb.Read(addrman))
             LogPrintf("Loaded %i addresses from peers.dat  %dms\n", addrman.size(), GetTimeMillis() - nStart);
         else {
+            addrman.Clear(); // Addrman can be in an inconsistent state after failure, reset it
             LogPrintf("Invalid or missing peers.dat; recreating\n");
             DumpAddresses();
         }
@@ -2336,6 +2337,11 @@ bool CAddrDB::Read(CAddrMan& addr)
     if (hashIn != hashTmp)
         return error("%s: Checksum mismatch, data corrupted", __func__);
 
+    return Read(addr, ssPeers);
+}
+
+bool CAddrDB::Read(CAddrMan& addr, CDataStream& ssPeers)
+{
     unsigned char pchMsgTmp[4];
     try {
         // de-serialize file header (network specific magic number) and ..
@@ -2349,6 +2355,8 @@ bool CAddrDB::Read(CAddrMan& addr)
         ssPeers >> addr;
     }
     catch (const std::exception& e) {
+        // de-serialization has failed, ensure addrman is left in a clean state
+        addr.Clear();
         return error("%s: Deserialize or I/O error - %s", __func__, e.what());
     }