UI: Fix button callback in OBSPropertiesView created with an id

Before calling the button callback, two values are null-checked but when
the property is created with an id (const char*). Those values are null
which prevent the callback from being called.
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Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f