Fixed the parsing of an undeclared template specialisation with an extension method.

Signed-off-by: Dimitar Dobrev <dpldobrev@protonmail.com>

src/Generator/Passes/TrimSpecializationsPass.cs

@@ -92,7 +92,8 @@ namespace CppSharp.Passes
         private void CleanSpecializations(Class template)
         {
             template.Specializations.RemoveAll(s =>
-                !specializations.Contains(s) && !internalSpecializations.Contains(s));
+                s.SpecializationKind == TemplateSpecializationKind.Undeclared ||
+                (!specializations.Contains(s) && !internalSpecializations.Contains(s)));
 
             foreach (var specialization in template.Specializations.Where(
                 s => s is ClassTemplatePartialSpecialization))

tests/CSharp/CSharpTemplates.h

@@ -318,6 +318,7 @@ public:
     T& operator[](const char* string);
 private:
     T t[1];
+    HasDefaultTemplateArgument<char> h;
 };
 
 template <typename T>