Revert to the old, arguably broken code for QT4 port selection, as QT4 doesn't support TCP socket binding as QT5 does.

runtime/pgAdmin4.cpp

@@ -68,8 +68,13 @@ int main(int argc, char * argv[])
     // Hence - putting this code in a code block so the scope of the socket
     // variable vanishes to make that socket available.
     {
+#if QT_VERSION >= 0x050000
         QTcpSocket socket;
         socket.bind(0, QTcpSocket::ShareAddress);
+#else
+        QUdpSocket socket;
+        socket.bind(0, QUdpSocket::ShareAddress);
+#endif
         port = socket.localPort();
     }