During migration, only do MangaController replacement if previous controller is also MangaController (#5869)

If previous controller is instead a MigrationController/other, push the new MangaController onto the stack instead

app/src/main/java/eu/kanade/tachiyomi/ui/browse/migration/search/SearchController.kt

@@ -75,8 +75,14 @@ class SearchController(
         if (!isReplacingManga) {
             router.popController(this)
             if (newManga != null) {
-                // Replaces old MangaController
-                router.replaceTopController(RouterTransaction.with(MangaController(newManga)))
+                val newMangaController = RouterTransaction.with(MangaController(newManga))
+                if (router.backstack.last().controller is MangaController) {
+                    // Replace old MangaController
+                    router.replaceTopController(newMangaController)
+                } else {
+                    // Push MangaController on top of MigrationController
+                    router.pushController(newMangaController)
+                }
             }
         }
     }