kivy: use app.num_chain

gui/kivy/main_window.py

@@ -80,6 +80,7 @@ class ElectrumWindow(App):
     num_nodes = NumericProperty(0)
     server_host = StringProperty('')
     server_port = StringProperty('')
+    num_chains = NumericProperty(0)
     blockchain_name = StringProperty('')
     blockchain_checkpoint = NumericProperty(0)
 
@@ -594,6 +595,7 @@ class ElectrumWindow(App):
 
     def on_network(self, event, *args):
         chain = self.network.blockchain()
+        self.num_chains = len(self.network.get_blockchains())
         self.blockchain_checkpoint = chain.get_checkpoint()
         self.blockchain_name = chain.get_name()
         if self.network.interface:

gui/kivy/uix/ui_screens/network.kv

@@ -46,8 +46,8 @@ Popup:
 
                 CardSeparator
                 SettingsItem:
-                    title: _('Fork detected at block %d')%app.blockchain_checkpoint if app.blockchain_checkpoint else _('No fork detected')
+                    title: _('Fork detected at block %d')%app.blockchain_checkpoint if app.num_chains>1 else _('No fork detected')
                     fork_description: (_('You are following branch') if app.auto_connect else _("Your server is on branch")) + ' ' + app.blockchain_name
-                    description: self.fork_description if app.blockchain_checkpoint else ''
+                    description: self.fork_description if app.num_chains>1 else _('Connected nodes are on the same chain')
                     action: app.choose_blockchain_dialog
-                    disabled: app.blockchain_checkpoint == 0
+                    disabled: app.num_chains == 1