Code Quality: Fixed possible ArgumentOutOfRangeException (#13656)

Author: hishitetsu

src/Files.App/Data/Contexts/Multitasking/MultitaskingContext.cs

@@ -17,8 +17,8 @@ internal class MultitaskingContext : ObservableObject, IMultitaskingContext
 		private ushort tabCount = 0;
 		public ushort TabCount => tabCount;
 
-		public TabBarItem CurrentTabItem => MainPageViewModel.AppInstances[currentTabIndex];
-		public TabBarItem SelectedTabItem => MainPageViewModel.AppInstances[selectedTabIndex];
+		public TabBarItem CurrentTabItem => MainPageViewModel.AppInstances.ElementAtOrDefault(currentTabIndex);
+		public TabBarItem SelectedTabItem => MainPageViewModel.AppInstances.ElementAtOrDefault(selectedTabIndex);
 
 		private ushort currentTabIndex = 0;
 		public ushort CurrentTabIndex => currentTabIndex;