Fix warnings for single instance handling

ILSpy/App.xaml.cs

@@ -104,9 +104,11 @@ namespace ICSharpCode.ILSpy
 			}
 		}
 
-		private static void SingleInstance_NewInstanceDetected(object? sender, NewInstanceEventArgs e)
+		private static void SingleInstance_NewInstanceDetected(object sender, NewInstanceEventArgs e)
 		{
+#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
 			ICSharpCode.ILSpy.MainWindow.Instance.HandleSingleInstanceCommandLineArguments(e.Args);
+#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
 		}
 
 		static Assembly ResolvePluginDependencies(AssemblyLoadContext context, AssemblyName assemblyName)

ILSpy/AppEnv/CommandLineArguments.cs

@@ -108,7 +108,7 @@ namespace ICSharpCode.ILSpy.AppEnv
 						instance.AssembliesToLoad.Add(assembly);
 				}
 			}
-			catch (Exception ex)
+			catch (Exception)
 			{
 				// Intentionally ignore exceptions if any, this is only added to always have an exception-free startup
 			}

ILSpy/AppEnv/SingleInstance.cs

@@ -14,6 +14,8 @@
 //2008-01-03: Added Resources
 //2007-12-29: New version
 
+#nullable enable
+
 namespace Medo.Application;
 
 using System;