fix: start filters insensitive if tree is empty

dzgui/controllers/emitter.py

@@ -60,6 +60,11 @@ class Emitter(GObject.GObject):
     def check_button_pressed(self, keyval: int) -> None:
         """User toggled filter panel check button via keyboard"""
 
+    @GObject.Signal(flags=GObject.SignalFlags.RUN_LAST, arg_types=(object,))
+    def server_page_changed(self, keyval: int) -> None:
+        """Triggered on 'switch-page' signal within tabs of NotebookPage.SERVERS."""
+        pass
+
     @GObject.Signal(flags=GObject.SignalFlags.RUN_LAST, arg_types=(bool,))
     def server_page_toggled(self, keyval: int) -> None:
         """Triggered on map/unmap signal from NotebookPage.SERVERS. Shows/hides grid panels."""