Fix #162 Opening a file that's not a valid assembly displays exception stack trace

ILSpy/LoadedAssembly.cs

@@ -211,6 +211,10 @@ namespace ICSharpCode.ILSpy
 			return this.assemblyTask.ContinueWith(onAssemblyLoaded, taskScheduler);
 		}
 		
+		/// <summary>
+		/// Wait until the assembly is loaded.
+		/// Throws an AggregateException when loading the assembly fails.
+		/// </summary>
 		public void WaitUntilLoaded()
 		{
 			assemblyTask.Wait();

ILSpy/TreeNodes/AssemblyTreeNode.cs

@@ -195,7 +195,17 @@ namespace ICSharpCode.ILSpy.TreeNodes
 
 		public override void Decompile(Language language, ITextOutput output, DecompilationOptions options)
 		{
-			assembly.WaitUntilLoaded(); // necessary so that load errors are passed on to the caller
+			try {
+				assembly.WaitUntilLoaded(); // necessary so that load errors are passed on to the caller
+			} catch (AggregateException ex) {
+				language.WriteCommentLine(output, assembly.FileName);
+				if (ex.InnerException is BadImageFormatException) {
+					language.WriteCommentLine(output, "This file does not contain a managed assembly.");
+					return;
+				} else {
+					throw;
+				}
+			}
 			language.DecompileAssembly(assembly, output, options);
 		}