Sanitize the scanlator in chapter download folder names

A "/" in the scanlator nested the chapter in a folder of its own, where the download was never found again. Names built from the unsanitized scanlator are still looked up.

app/src/main/java/eu/kanade/tachiyomi/data/download/DownloadProvider.kt

@@ -168,10 +168,13 @@ class DownloadProvider(
         chapterUrl: String,
         disallowNonAsciiFilenames: Boolean = libraryPreferences.disallowNonAsciiFilenames.get(),
         enableChapterNameHash: Boolean = libraryPreferences.enableChapterNameHash.get(),
+        sanitizeScanlator: Boolean = true,
     ): String {
         return buildString {
             if (!chapterScanlator.isNullOrBlank()) {
-                append(chapterScanlator + "_")
+                // A "/" in the scanlator would otherwise nest the chapter in a folder of its own
+                append(if (sanitizeScanlator) DiskUtil.buildValidFilename(chapterScanlator) else chapterScanlator)
+                append("_")
             }
 
             // Subtract 7 bytes for hash and underscore, 4 bytes for .cbz
@@ -226,11 +229,28 @@ class DownloadProvider(
                 )
             }
 
+        // Scanlators weren't sanitized for a while. One with a "/" nested its folder, so it was never found anyway.
+        val unsanitizedScanlatorChapterDirNames = if (chapterScanlator != null && '/' !in chapterScanlator) {
+            booleanPairPermutation.map { (disallowNonAsciiFilenames, enableChapterNameHash) ->
+                getChapterDirName(
+                    chapterName,
+                    chapterScanlator,
+                    chapterUrl,
+                    disallowNonAsciiFilenames,
+                    enableChapterNameHash,
+                    sanitizeScanlator = false,
+                )
+            }
+        } else {
+            emptyList()
+        }
+
         return buildSet {
             // Chapter name without hash (unable to handle duplicate
             // chapter names)
             add(chapterNameV1)
             addAll(othersChapterDirNames)
+            addAll(unsanitizedScanlatorChapterDirNames)
         }
     }