Flip left/right key events for Webtoon viewer (fixes #4111)

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

@@ -293,11 +293,11 @@ class WebtoonViewer(val activity: ReaderActivity, val isContinuous: Boolean = tr
             }
             KeyEvent.KEYCODE_MENU -> if (isUp) activity.toggleMenu()
 
-            KeyEvent.KEYCODE_DPAD_RIGHT,
+            KeyEvent.KEYCODE_DPAD_LEFT,
             KeyEvent.KEYCODE_DPAD_UP,
             KeyEvent.KEYCODE_PAGE_UP -> if (isUp) scrollUp()
 
-            KeyEvent.KEYCODE_DPAD_LEFT,
+            KeyEvent.KEYCODE_DPAD_RIGHT,
             KeyEvent.KEYCODE_DPAD_DOWN,
             KeyEvent.KEYCODE_PAGE_DOWN -> if (isUp) scrollDown()
             else -> return false