doc: Fix Misleading Error Message for multiclass_precision

[adrianjoshua-strutt]

Old message was somewhat misleading. It implies that there are always zero instances for classes in both predictions and ground truth labels.

Summary:
To make error more clear change message from

classes have zero instances in both the predictions and the ground truth labels. Precision is still logged as zero.

to

classes have zero instances in either the predictions or the ground truth labels. Precision is still logged as zero.

Fixes #{198}
Issue

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