Random potential crash fixes

app/src/main/java/eu/kanade/tachiyomi/ui/category/CategoryPresenter.kt

@@ -73,7 +73,7 @@ class CategoryPresenter(
         val cat = Category.create(name)
 
         // Set the new item in the last position.
-        cat.order = categories.maxOf { it.order } + 1
+        cat.order = (categories.maxOfOrNull { it.order } ?: 0) + 1
 
         // Insert into database.
         cat.mangaSort = LibrarySort.Title.categoryValue

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

@@ -72,7 +72,7 @@ class LibraryCategoryAdapter(val controller: LibraryController) :
     fun findCategoryHeader(catId: Int): LibraryHeaderItem? {
         return currentItems.find {
             (it is LibraryHeaderItem) && it.category.id == catId
-        } as LibraryHeaderItem
+        } as? LibraryHeaderItem
     }
 
     /**