Fix library settings sheet causing app to crash... (#5354)

...when the category list is empty

app/src/main/java/eu/kanade/tachiyomi/ui/library/LibraryController.kt

@@ -262,9 +262,13 @@ class LibraryController(
     }
 
     fun showSettingsSheet() {
+        if (adapter?.categories?.isNotEmpty() == true) {
             adapter?.categories?.get(binding.libraryPager.currentItem)?.let { category ->
                 settingsSheet?.show(category)
             }
+        } else {
+            settingsSheet?.show()
+        }
     }
 
     fun onNextLibraryUpdate(categories: List<Category>, mangaMap: Map<Int, List<LibraryItem>>) {