[Semantics] ConversionResolveResult: For nullable conversions return

the constant value of the input resolve result. IMHO ConstantValue ==
null is an error for example for int? i = 1; case. The constant value
should be '1' there.

ICSharpCode.NRefactory/Semantics/ConversionResolveResult.cs

@@ -63,5 +63,13 @@ namespace ICSharpCode.NRefactory.Semantics
 		{
 			return new [] { Input };
 		}
+
+		public override object ConstantValue {
+			get { 
+				if (Conversion.IsNullableConversion)
+					return Input.ConstantValue;
+				return null;
+			}
+		}
 	}
 }