Wrong handling of unsupported protocol, added a test for it.

Author: fbacchella

src/main/java/zmq/SocketBase.java

@@ -213,7 +213,7 @@ private NetProtocol checkProtocol(String protocol)
             NetProtocol proto = NetProtocol.getProtocol(protocol);
             if (!proto.isValid()) {
                 errno.set(ZError.EPROTONOSUPPORT);
-                return proto;
+                return null;
             }
 
             //  Check whether socket type and transport protocol match.

src/test/java/zmq/TestUnsupported.java

@@ -0,0 +1,43 @@
+package zmq;
+
+import java.util.List;
+import java.util.function.Predicate;
+
+import org.junit.After;
+import org.junit.Test;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.MatcherAssert.assertThat;
+
+public class TestUnsupported
+{
+    Ctx ctx = ZMQ.init(1);
+
+    @After
+    public void close()
+    {
+        ctx.terminate();
+    }
+
+    private void doOperation(Predicate<SocketBase> networkOperation)
+    {
+        SocketBase socket = ZMQ.socket(ctx, ZMQ.ZMQ_SERVER);
+        try {
+            boolean rc = networkOperation.test(socket);
+            assertThat(rc, is(false));
+            assertThat(socket.errno.get(), is(ZError.EPROTONOSUPPORT));
+        }
+        finally {
+            socket.close();
+        }
+    }
+
+    @Test(timeout = 100)
+    public void doTests()
+    {
+        for (String proto : List.of("pgm", "epgm", "norm", "ws", "wss", "tipc", "vmci")) {
+            doOperation(s -> s.connect(proto + "://localhost:*"));
+            doOperation(s -> s.bind(proto + "://localhost:*"));
+        }
+    }
+}