Fix #3545: Covariant return not detected for abstract override property

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

@@ -1,5 +1,16 @@
 namespace ICSharpCode.Decompiler.Tests.TestCases.CovariantReturns
 {
+	public abstract class AbstractDerived : Base
+	{
+		public abstract override AbstractDerived Instance { get; }
+
+		public abstract override AbstractDerived this[int index] { get; }
+
+		public abstract override AbstractDerived Build();
+
+		protected abstract override AbstractDerived SetParent(object parent);
+	}
+
 	public abstract class Base
 	{
 		public abstract Base Instance { get; }

ICSharpCode.Decompiler/CSharp/CSharpDecompiler.cs

@@ -2126,7 +2126,7 @@ namespace ICSharpCode.Decompiler.CSharp
 				{
 					SetNewModifier(propertyDecl);
 				}
-				if (getterHasBody && IsCovariantReturnOverride(property.Getter))
+				if (IsCovariantReturnOverride(property.Getter))
 				{
 					RemoveAttribute(getter, KnownAttribute.PreserveBaseOverrides);
 					propertyDecl.Modifiers &= ~(Modifiers.New | Modifiers.Virtual);