fixes an issue where byref wasnt properly handled when using it in a generic param (#22337)

* fixes an issue where byref wasnt properly handled when using it in a generic param

* removes unreachable check

tests/cpp/tpassbypragmas.nim

@@ -0,0 +1,27 @@
+discard """
+  targets: "cpp"
+  cmd: "nim cpp $file"
+"""
+{.emit:"""/*TYPESECTION*/
+
+  template<typename T>
+  struct Box {
+      T first;
+  };
+  struct Foo {
+  void test(void (*func)(Box<Foo>& another)){
+
+    };
+  };
+""".}
+
+type 
+  Foo {.importcpp.} = object
+  Box[T] {.importcpp:"Box<'0>".} = object
+    first: T
+
+proc test(self: Foo, fn: proc(another {.byref.}: Box[Foo]) {.cdecl.}) {.importcpp.}
+
+proc fn(another {.byref.} : Box[Foo]) {.cdecl.} = discard
+
+Foo().test(fn)