fix copy-paste error in PeekOrDefault extension

ICSharpCode.Decompiler/IL/ILReader.cs

@@ -151,7 +151,7 @@ namespace ICSharpCode.Decompiler.IL
 		/// </summary>
 		void Warn(string message)
 		{
-			//Debug.Fail(message);
+			Debug.Fail(message);
 		}
 
 		void ReadInstructions(Dictionary<int, ImmutableArray<StackType>> outputStacks, CancellationToken cancellationToken)

ICSharpCode.Decompiler/IL/Instructions/BinaryNumericInstruction.cs

@@ -59,6 +59,7 @@ namespace ICSharpCode.Decompiler.IL
 			this.Sign = sign;
 			this.CompoundAssignmentType = compoundAssignmentType;
 			this.resultType = ComputeResultType(opCode, left.ResultType, right.ResultType);
+			Debug.Assert(resultType != StackType.Unknown);
 			Debug.Assert(CompoundAssignmentType == CompoundAssignmentType.None || IsValidCompoundAssignmentTarget(Left));
 		}
 		

ICSharpCode.Decompiler/Util/CollectionExtensions.cs

@@ -19,7 +19,7 @@ namespace ICSharpCode.Decompiler
 		{
 			if (stack.Count == 0)
 				return default(T);
-			return stack.Pop();
+			return stack.Peek();
 		}
 		
 		public static void AddRange<T>(this ICollection<T> collection, IEnumerable<T> input)