avoid two NPEs on corrupt fragments

router/java/src/net/i2p/router/tunnel/FragmentHandler.java

@@ -372,6 +372,8 @@ public class FragmentHandler {
             int fragmentCount = msg.getFragmentCount();
             // toByteArray destroys the contents of the message completely
             byte data[] = msg.toByteArray();
+            if (data == null)
+                throw new I2NPMessageException("null data");   // fragments already released???
             if (_log.shouldLog(Log.DEBUG))
                 _log.debug("RECV(" + data.length + "): " + Base64.encode(data)  
                            + " " + _context.sha().calculateHash(data).toBase64());

router/java/src/net/i2p/router/tunnel/FragmentedMessage.java

@@ -189,6 +189,9 @@ public class FragmentedMessage {
         int size = 0;
         for (int i = 0; i <= _highFragmentNum; i++) {
             ByteArray ba = _fragments[i];
+            // NPE seen here, root cause unknown
+            if (ba == null) 
+                throw new IllegalStateException("wtf, don't get the completed size when we're not complete - null fragment i=" + i + " of " + _highFragmentNum);
             size += ba.getValid();
         }
         return size;