qml network: restrict cases where server is shown "lagging"

electrum/gui/qml/components/NetworkOverview.qml

@@ -69,11 +69,11 @@ Pane {
                 Label {
                     text: qsTr('Server Height:');
                     color: Material.accentColor
-                    visible: Network.serverHeight != Network.height
+                    visible: Network.serverHeight != 0 && Network.serverHeight < Network.height
                 }
                 Label {
                     text: Network.serverHeight + " (lagging)"
-                    visible: Network.serverHeight != Network.height
+                    visible: Network.serverHeight != 0 && Network.serverHeight < Network.height
                 }
                 Heading {
                     Layout.columnSpan: 2

electrum/network.py

@@ -1218,7 +1218,7 @@ class Network(Logger, NetworkRetryManager[ServerAddr]):
         interface = self.interface
         return interface.tip if interface else 0
 
-    def get_local_height(self):
+    def get_local_height(self) -> int:
         """Length of header chain, POW-verified.
         In case of a chain split, this is for the branch the main interface is on,
         but it is the tip of that branch (even if main interface is behind).