Fix NRE with tuple discards in DeconstructionTransform

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

@@ -216,5 +216,10 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 		{
 			(Get(0).NMy, Get(1).My) = GetTuple<MyInt?, MyInt>();
 		}
+
+		public void Tuple_Property_NoConversion_DiscardLast()
+		{
+			(Get(0).NMy, Get(1).My, _) = GetTuple<MyInt?, MyInt, int>();
+		}
 	}
 }

ICSharpCode.Decompiler/IL/Transforms/DeconstructionTransform.cs

@@ -209,8 +209,15 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 				IsDeconstructTuple = this.tupleType != null
 			};
 			int index = 0;
-			foreach (ILVariable result in deconstructionResults) {
-				result.Kind = VariableKind.PatternLocal;
+			foreach (ILVariable v in deconstructionResults) {
+				var result = v;
+				if (result == null) {
+					var freshVar = new ILVariable(VariableKind.PatternLocal, this.tupleType.ElementTypes[index]) { Name = "E_" + index };
+					context.Function.Variables.Add(freshVar);
+					result = freshVar;
+				} else {
+					result.Kind = VariableKind.PatternLocal;
+				}
 				replacement.Pattern.SubPatterns.Add(
 					new MatchInstruction(
 						result,