Add a clarifying comment to shouldContinueLoading handling.

PiperOrigin-RevId: 289424321

library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImplInternal.java

@@ -1769,6 +1769,8 @@ import java.util.concurrent.atomic.AtomicBoolean;
       }
     }
     if (shouldContinueLoading) {
+      // We should still be loading, except in the case that it's no longer possible (i.e., because
+      // we've loaded the current playlist to the end).
       shouldContinueLoading = isLoadingPossible();
       updateIsLoading();
     } else {