Fix local source cover changing (#6252)

* fix local source cover changing

* Remove unnecessary check for `exists()`

* fix for when there is no thumbnail_url in the db

app/src/main/java/eu/kanade/tachiyomi/source/LocalSource.kt

@@ -56,15 +56,14 @@ class LocalSource(private val context: Context) : CatalogueSource {
             if (cover == null) {
                 cover = File("${dir.absolutePath}/${manga.url}", COVER_NAME)
             }
-            if (!cover.exists()) {
-                // It might not exist if using the external SD card
-                cover.parentFile?.mkdirs()
-                input.use {
-                    cover.outputStream().use {
-                        input.copyTo(it)
-                    }
+            // It might not exist if using the external SD card
+            cover.parentFile?.mkdirs()
+            input.use {
+                cover.outputStream().use {
+                    input.copyTo(it)
                 }
             }
+            manga.thumbnail_url = cover.absolutePath
             return cover
         }