Fix cancelAll() termination condition

The method cancellAll() was using the field maxPreload to determine when the for loop should terminate, which was always off by one compared to the size of the preloadTargetQueue, and therefore, not all the pre-loaded requests would be canceled. This issue was raised in #3693

Author: paynemiller92

library/src/main/java/com/bumptech/glide/ListPreloader.java

@@ -219,7 +219,7 @@ private void preloadItem(@Nullable T item, int position, int perItemPosition) {
   }
 
   private void cancelAll() {
-    for (int i = 0; i < maxPreload; i++) {
+    for (int i = 0; i < preloadTargetQueue.queue.size(); i++) {
       requestManager.clear(preloadTargetQueue.next(0, 0));
     }
   }