Fix webtoon viewer pages not loading

Partial revert of fddca15182

app/src/main/java/eu/kanade/tachiyomi/ui/reader/viewer/webtoon/WebtoonPageHolder.kt

@@ -246,19 +246,19 @@ class WebtoonPageHolder(
         unsubscribeReadImageHeader()
         val streamFn = page?.stream ?: return
 
+        var openStream: InputStream? = null
         readImageHeaderSubscription = Observable
             .fromCallable {
                 val stream = streamFn().buffered(16)
-                val imageStream = process(stream)
-                val isAnimated = ImageUtil.isAnimatedAndSupported(stream)
-                Pair(imageStream, isAnimated)
+                openStream = process(stream)
+
+                ImageUtil.isAnimatedAndSupported(stream)
             }
             .subscribeOn(Schedulers.io())
             .observeOn(AndroidSchedulers.mainThread())
-            .doOnNext { (imageStream, isAnimated) ->
-                imageStream.use {
+            .doOnNext { isAnimated ->
                 frame.setImage(
-                        it,
+                    openStream!!,
                     isAnimated,
                     ReaderPageImageView.Config(
                         zoomDuration = viewer.config.doubleTapAnimDuration,
@@ -267,7 +267,9 @@ class WebtoonPageHolder(
                     ),
                 )
             }
-            }
+            // Keep the Rx stream alive to close the input stream only when unsubscribed
+            .flatMap { Observable.never<Unit>() }
+            .doOnUnsubscribe { openStream?.close() }
             .subscribe({}, {})
 
         addSubscription(readImageHeaderSubscription)