[UI] Fix leaked locked_achievement_icon_ texture on drawer teardown

Reset locked_achievement_icon_ alongside font_texture_ and
notification_icon_textures_ when the immediate drawer is cleared,
preventing a debug assertion in D3D12ImmediateDrawer's destructor.

src/xenia/ui/imgui_drawer.cc

@@ -564,7 +564,7 @@ void ImGuiDrawer::SetImmediateDrawer(ImmediateDrawer* new_immediate_drawer) {
   if (immediate_drawer_) {
     GetIO().Fonts->TexID = reinterpret_cast<ImTextureID>(nullptr);
     font_texture_.reset();
-
+    locked_achievement_icon_.reset();
     notification_icon_textures_.clear();
   }
   immediate_drawer_ = new_immediate_drawer;