Fix naming of stack slots generated by ILReader.Push.

ICSharpCode.Decompiler/IL/ILReader.cs

@@ -880,6 +880,7 @@ namespace ICSharpCode.Decompiler.IL
 			IType type = compilation.FindType(inst.ResultType.ToKnownTypeCode());
 			var v = new ILVariable(VariableKind.StackSlot, type, inst.ResultType, inst.ILRange.Start);
 			v.Name = "S_" + inst.ILRange.Start.ToString("x4");
+			v.HasGeneratedName = true;
 			currentStack = currentStack.Push(v);
 			return new StLoc(v, inst);
 		}

ICSharpCode.Decompiler/IL/ILVariable.cs

@@ -267,6 +267,8 @@ namespace ICSharpCode.Decompiler.IL
 		
 		public ILVariable(VariableKind kind, IType type, StackType stackType, int index)
 		{
+			if (type == null)
+				throw new ArgumentNullException(nameof(type));
 			this.Kind = kind;
 			this.type = type;
 			this.StackType = stackType;