USBMS: Dismiss ConfirmBox on unplug

Fix #8112

frontend/ui/elements/mass_storage.lua

@@ -55,7 +55,7 @@ function MassStorage:start(never_ask)
 
     if not never_ask and self:requireConfirmation() then
         local ConfirmBox = require("ui/widget/confirmbox")
-        UIManager:show(ConfirmBox:new{
+        self.usbms_widget = ConfirmBox:new{
             text = _("Share storage via USB?"),
             ok_text = _("Share"),
             ok_callback = function()
@@ -65,7 +65,12 @@ function MassStorage:start(never_ask)
                 UIManager:broadcastEvent(Event:new("Close"))
                 UIManager:quit()
             end,
-        })
+            cancel_callback = function()
+                self:dismiss()
+            end,
+        }
+
+        UIManager:show(self.usbms_widget)
     else
         -- save settings before activating USBMS:
         UIManager:flushSettings()
@@ -75,4 +80,14 @@ function MassStorage:start(never_ask)
     end
 end
 
+-- Dismiss the ConfirmBox
+function MassStorage:dismiss()
+    if not self.usbms_widget then
+        return
+    end
+
+    UIManager:close(self.usbms_widget)
+    self.usbms_widget = nil
+end
+
 return MassStorage

frontend/ui/uimanager.lua

@@ -212,6 +212,10 @@ function UIManager:init()
             self:_afterNotCharging()
             if Device.screen_saver_mode then
                 self:suspend()
+            else
+                -- Potentially dismiss the USBMS ConfirmBox
+                local MassStorage = require("ui/elements/mass_storage")
+                MassStorage:dismiss()
             end
         end
         self.event_handlers["__default__"] = function(input_event)
@@ -366,6 +370,10 @@ function UIManager:init()
             self:_afterNotCharging()
             if Device.screen_saver_mode then
                 self:suspend()
+            else
+                -- Potentially dismiss the USBMS ConfirmBox
+                local MassStorage = require("ui/elements/mass_storage")
+                MassStorage:dismiss()
             end
         end
         self.event_handlers["__default__"] = function(input_event)