Bug: Second ID missing in player games comparison results in avalanche of errors

[IndexLibrorumProhibitorum]

Running the new function to check if two ID's have shared games creates a large number of error warning popups if the second ID input field is empty.

[magge-faf]

I can catch that exception, so no error pops up in the next version - You need to provide two player IDs to make use of that 'Check' method.

[IndexLibrorumProhibitorum]

Also happens when both fields are empty, I've noticed :)

Didn't intend to trigger either of the two, but misclicked a button.