Fix #2202: prevent casting null to void* if the expected target-type is (U)IntPtr?

ICSharpCode.Decompiler.Tests/TestCases/Pretty/ConstantsTests.cs

@@ -1,9 +1,20 @@
-using System.Threading.Tasks;
+using System;
+using System.Threading.Tasks;
 
 namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 {
 	internal class ConstantsTests
 	{
+		public IntPtr? NullableIntPtr()
+		{
+			return null;
+		}
+
+		public UIntPtr? NullableUIntPtr()
+		{
+			return null;
+		}
+
 		public ulong Issue1308(ulong u = 8uL)
 		{
 			Test((u & 0xFFFFFFFFu) != 0);

ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs

@@ -351,7 +351,7 @@ namespace ICSharpCode.Decompiler.CSharp
 						.ConvertTo(targetType, expressionBuilder, checkForOverflow, allowImplicitConversion);
 				}
 			}
-			if (targetUType.IsKnownType(KnownTypeCode.IntPtr))
+			if (targetUType.IsKnownType(KnownTypeCode.IntPtr) && utype.GetStackType().IsIntegerType())
 			{ // Conversion to IntPtr
 				if (type.IsKnownType(KnownTypeCode.Int32) || type.Kind == TypeKind.NInt)
 				{
@@ -382,7 +382,7 @@ namespace ICSharpCode.Decompiler.CSharp
 						.ConvertTo(targetType, expressionBuilder, checkForOverflow);
 				}
 			}
-			else if (targetUType.IsKnownType(KnownTypeCode.UIntPtr))
+			else if (targetUType.IsKnownType(KnownTypeCode.UIntPtr) && utype.GetStackType().IsIntegerType())
 			{ // Conversion to UIntPtr
 				if (type.IsKnownType(KnownTypeCode.UInt32) || type.Kind.IsAnyPointer() || type.Kind == TypeKind.NUInt)
 				{