Fix label printing order

[jacobmanning]

There is a bug here causing predicted labels to be printed in incorrect order. Traversing a java.util.PriorityQueue with a range-based for loop does not guarantee traversal in sorted order. Fixed by converting PQ to array, sorting array with PQ.comparator(), and returning the results in sorted order.

More information on the undefined behavior of traversing PQ here.

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[jacobmanning]

@googlebot I signed it!

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