Navigate back from episodes with 'edge-overshot' signal

But only do so if on mobile. Compensates for lack of swipes in
TreeViews.

share/gpodder/ui/adaptive/gpodder.ui

@@ -347,10 +347,11 @@
                           </packing>
                         </child>
                         <child>
-                          <object class="GtkScrolledWindow">
+                          <object class="GtkScrolledWindow" id="episodes_scrolled_window">
                             <property name="visible">True</property>
                             <property name="can-focus">True</property>
                             <property name="vexpand">True</property>
+                            <property name="vscrollbar-policy">always</property>
                             <property name="shadow-type">in</property>
                             <child>
                               <object class="GtkTreeView" id="treeAvailable">

src/gpodder/gtkui/main.py

@@ -52,7 +52,7 @@ from .draw import (cake_size_from_widget, draw_cake_pixbuf,
                    draw_iconcell_scale, draw_text_box_centered)
 from .interface.addpodcast import gPodderAddPodcast
 from .interface.common import (BuilderWidget, Dummy, ExtensionMenuHelper,
-                               TreeViewHelper)
+                               TreeViewHelper, is_on_mobile_screen)
 from .interface.progress import ProgressIndicator
 from .interface.searchtree import SearchTreeBar
 from .model import EpisodeListModel, PodcastChannelProxy, PodcastListModel
@@ -299,6 +299,11 @@ class gPodder(BuilderWidget, dbus.service.Object):
 
         self.treeChannels.grab_focus()
 
+        # Swipe up to go back hack for episodes leaflet page
+        if is_on_mobile_screen(self.main_window):
+            self.episodes_scrolled_window.connect(
+                'edge-overshot', self.on_episodes_scrolled_window_edge_overshot)
+
         # First-time users should be asked if they want to see the OPML
         if self.options.subscribe:
             util.idle_add(self.subscribe_to_url, self.options.subscribe)
@@ -818,6 +823,10 @@ class gPodder(BuilderWidget, dbus.service.Object):
         ev = Dummy(x=x, y=y, button=3)
         return self.treeview_available_show_context_menu(ev)
 
+    def on_episodes_scrolled_window_edge_overshot(self, scrolled_window, pos, *args):
+        if pos == Gtk.PositionType.TOP:
+            self.leaflet.navigate(Handy.NavigationDirection.BACK)
+
     def on_treeview_downloads_button_released(self, treeview, event):
         if event.window != treeview.get_bin_window():
             return False