fixes #7600, generic object with generic ref object parent typerel bug (#7678)

* fixes #7600

* fix wrong logic

tests/typerel/t7600_1.nim

@@ -0,0 +1,18 @@
+discard """
+errormsg: "type mismatch: got <Thin[system.int]>"
+nimout: '''t7600_1.nim(18, 6) Error: type mismatch: got <Thin[system.int]>
+but expected one of:
+proc test[T](x: Paper[T])
+
+expression: test tn'''
+"""
+
+type
+  Paper[T] = ref object of RootObj
+    thickness: T
+  Thin[T]  = object of Paper[T]
+
+proc test[T](x: Paper[T]) = discard
+
+var tn = Thin[int]()
+test tn

tests/typerel/t7600_2.nim

@@ -0,0 +1,17 @@
+discard """
+errormsg: "type mismatch: got <Thin>"
+nimout: '''t7600_2.nim(17, 6) Error: type mismatch: got <Thin>
+but expected one of:
+proc test(x: Paper)
+
+expression: test tn'''
+"""
+
+type
+  Paper = ref object of RootObj
+  Thin  = object of Paper
+
+proc test(x: Paper) = discard
+
+var tn = Thin()
+test tn