Network: Fix window duplication prohibition mechanism.

src/View/MainWindow.py

@@ -490,10 +490,12 @@ class ApplicationWindow(QMainWindow, ListedSubWindow, WindowToolKit):
         Returns:
             Nothing
         """
-        if (self.model is not None and
-            not self.sub_win_exists("River network")):
-            self.network = NetworkWindow(model=self.model, parent=self)
-            self.network.show()
+        if self.model is not None:
+            if not self.sub_win_exists("River network"):
+                self.network = NetworkWindow(model=self.model, parent=self)
+                self.network.show()
+            else:
+                self.network.activateWindow()
 
     def open_geometry(self):
         """Open geometry window