Ensure the OP_WRITE subscription can't get left on

Unclear how, but it seems that it is still possible for this to happen.
Once it does, that channel spins 100% on the device until it closes, or
until we successfully write something else (and clear up afterwards).
Would be nice to find the root cause, but this solves the immediate
problem safely & clearly.

Author: pimterry

app/src/main/java/tech/httptoolkit/android/vpn/socket/SocketNIODataService.java

@@ -150,8 +150,6 @@ private void runTask(){
 
 				while (iterator.hasNext()) {
 					SelectionKey key = iterator.next();
-					SelectableChannel selectableChannel = key.channel();
-
 					Session session = ((Session) key.attachment());
 					synchronized (session) { // Sessions are locked during processing (no VPN data races)
 						try {
@@ -235,7 +233,10 @@ private void processSelectorRead(SelectionKey selectionKey, Session session) {
 
 	private void processPendingWrite(SelectionKey selectionKey, Session session) {
 		// Nothing to write? Skip this entirely, and make sure we're not subscribed
-		if (!session.hasDataToSend() || !session.isDataForSendingReady()) return;
+		if (!session.hasDataToSend() || !session.isDataForSendingReady()) {
+			session.unsubscribeKey(SelectionKey.OP_WRITE);
+			return;
+		}
 
 		boolean canWrite;
 		synchronized (selectionKey) {