enhance(library): Show "category is empty" on filtered if the category is actually empty

app/src/main/java/eu/kanade/tachiyomi/data/database/models/LibraryManga.kt

@@ -14,6 +14,13 @@ data class LibraryManga(
     var lastFetch: Int = 0,
 ) : MangaImpl() {
 
+    var realMangaCount = 0
+        get() = if (isBlank()) field else throw IllegalStateException("realMangaCount is only accessible for placeholders")
+        set(value) {
+            if (!isBlank()) throw IllegalStateException("realMangaCount can only be set for placeholders")
+            field = value
+        }
+
     val hasRead
         get() = read > 0
 

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

@@ -48,7 +48,7 @@ class LibraryListHolder(
                 binding.title.isVisible = false
             } else {
                 binding.title.text = itemView.context.getString(
-                    if (adapter.hasActiveFilters) {
+                    if (adapter.hasActiveFilters && item.manga.realMangaCount >= 1) {
                         R.string.no_matches_for_filters_short
                     } else {
                         R.string.category_is_empty

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

@@ -341,7 +341,12 @@ class LibraryPresenter(
             )
         hasActiveFilters = !filtersOff
         val missingCategorySet = categories.mapNotNull { it.id }.toMutableSet()
+        val realCount = mutableMapOf<Int, Int>()
         val filteredItems = this.filter f@{ item ->
+            if (showEmptyCategoriesWhileFiltering) {
+                realCount[item.manga.category] = sectionedLibraryItems[item.manga.category]?.size ?: 0
+            }
+
             if (!showEmptyCategoriesWhileFiltering && item.manga.isHidden()) {
                 val subItems = sectionedLibraryItems[item.manga.category]?.takeUnless { it.size <= 1 }
                     ?: hiddenLibraryItems.filter { it.manga.category == item.manga.category }
@@ -376,7 +381,9 @@ class LibraryPresenter(
         }.toMutableList()
         if (showEmptyCategoriesWhileFiltering) {
             missingCategorySet.forEach {
-                filteredItems.add(blankItem(it).first())
+                filteredItems.add(
+                    blankItem(it).first().apply { manga.realMangaCount = realCount[it] ?: 0 }
+                )
             }
         }
         return filteredItems