addrdb: Only call Serialize() once

The previous logic would call it once for serializing into the filestream,
and then again for serializing into the hasher. If AddrMan was changed
in between these calls by another thread, the resulting peers.dat would
be corrupt with non-matching checksum and data.
Fix this by using HashedSourceWriter, which writes the data
to the underlying stream and keeps track of the hash in one go.

Author: mzumsande

src/addrdb.cpp

@@ -34,10 +34,9 @@ bool SerializeDB(Stream& stream, const Data& data)
 {
     // Write and commit header, data
     try {
-        CHashWriter hasher(stream.GetType(), stream.GetVersion());
-        stream << Params().MessageStart() << data;
-        hasher << Params().MessageStart() << data;
-        stream << hasher.GetHash();
+        HashedSourceWriter hashwriter{stream};
+        hashwriter << Params().MessageStart() << data;
+        stream << hashwriter.GetHash();
     } catch (const std::exception& e) {
         return error("%s: Serialize or I/O error - %s", __func__, e.what());
     }

src/addrman.cpp

@@ -1178,8 +1178,7 @@ void AddrMan::Unserialize(Stream& s_)
 }
 
 // explicit instantiation
-template void AddrMan::Serialize(CHashWriter& s) const;
-template void AddrMan::Serialize(CAutoFile& s) const;
+template void AddrMan::Serialize(HashedSourceWriter<CAutoFile>& s) const;
 template void AddrMan::Serialize(CDataStream& s) const;
 template void AddrMan::Unserialize(CAutoFile& s);
 template void AddrMan::Unserialize(CHashVerifier<CAutoFile>& s);