fix #1265

TestSuite/generics24.pas

@@ -0,0 +1,13 @@
+type
+  at1 = abstract class
+    public constructor := exit;
+  end;
+
+procedure p1<T1>(o1: T1);
+where T1: at1;
+begin end;
+
+begin
+  var o: at1;
+  p1(o);
+end.

TreeConverter/TreeRealization/generics.cs

@@ -1334,6 +1334,8 @@ namespace PascalABCCompiler.TreeRealization
 
         public static bool type_has_default_ctor(type_node tn, bool find_protected_ctors)
         {
+            if (tn.is_generic_parameter && tn.base_type != null && tn.base_type.IsAbstract)
+                return false;
             List<SymbolInfo> sil = tn.find_in_type(compiler_string_consts.default_constructor_name, tn.Scope);
             if (sil != null)
             {