Fix #1524: Adjust expression trees transform to work with async code as well.

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

@@ -22,6 +22,7 @@ using System.Linq;
 using System.Linq.Expressions;
 using System.Reflection;
 using System.Threading;
+using System.Threading.Tasks;
 using System.Xml;
 
 namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
@@ -1026,6 +1027,23 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 				Field = 3
 			});
 		}
+
+		public async Task Issue1524(string str)
+		{
+			await Task.Delay(100);
+			if (string.IsNullOrEmpty(str)) {
+#if ROSLYN
+				if (int.TryParse(str, out int id)) {
+#else
+				int id;
+				if (int.TryParse(str, out id)) {
+#endif
+					(from a in new List<int>().AsQueryable()
+						where a == id
+						select a).FirstOrDefault();
+				}
+			}
+		}
 	}
 
 	internal static class Extensions

ICSharpCode.Decompiler/IL/Transforms/TransformExpressionTrees.cs

@@ -1072,9 +1072,7 @@ namespace ICSharpCode.Decompiler.IL.Transforms
 							return new LdLoca(v);
 						return null;
 					} else {
-						if (ldloc.Variable.Kind != VariableKind.StackSlot)
+						return ldloc;
-							return ldloc;
-						return null;
 					}
 				default:
 					return value.Clone();