Hi. I tested on both your site and my site and trying to add a zero quantity of WooCommerce tickets takes me to the WooCommerce Cart with a message that the cart is empty.
If you’re saying that you’d like to avoid this potential confusion and disallow clicking the button until the quantity is entered, here are some options:
1) Always set a quantity of 1:
https://gist.github.com/cliffordp/5b57df71be8b52f595817ddbf81acdab
2) Custom JS
You could add some custom JS to detect. I imagine the code snippet above could be used to point you in the right direction.
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And/Or you could request this as a new feature (or maybe search to see if the idea was already posted by someone else) at our plugins’ UserVoice page.
This allows others who are interested in that feature to easily voice their support. We frequently review suggestions there to find out which ones are popular, then we implement as many of them as we can.
If you post it / find it, feel free to link to it from here in case anyone comes across this forum thread in the future.