Anvil saver pads data to 4K boundaries.

Fixes #524.

src/WorldStorage/WSSAnvil.cpp

@@ -2672,6 +2672,11 @@ bool cWSSAnvil::cMCAFile::SetChunkData(const cChunkCoords & a_Chunk, const AStri
 		return false;
 	}
 	
+	// Add padding to 4K boundary:
+	size_t BytesWritten = a_Data.size() + MCA_CHUNK_HEADER_LENGTH;
+	static const char Padding[4095] = {0};
+	m_File.Write(Padding, 4096 - (BytesWritten % 4096));
+	
 	// Store the header:
 	ChunkSize = (a_Data.size() + MCA_CHUNK_HEADER_LENGTH + 4095) / 4096;  // Round data size *up* to nearest 4KB sector, make it a sector number
 	ASSERT(ChunkSize < 256);