Fix infinite loop when enabling callback without handlers #7
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When libssh2_session_callback_set() is used to activate a callback for which no handler was registered in libssh2_session_init_ex(), this can result in an infinite loop because the user event from lvssh2 is always registered automatically. When the callback is activated, it always returns default values because the VI refnum is undefined. This changes the implementation so that the LabVIEW user event is only created when a valid VI refnum is provided. The extension library returns an error if the user event does not exist, which effectively breaks any infinite loops.
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When libssh2_session_callback_set() is used to activate a callback for which no handler was registered in libssh2_session_init_ex(), this can result in an infinite loop because the user event from lvssh2 is always registered automatically. When the callback is activated, it always returns default values because the VI refnum is undefined.
This changes the implementation so that the LabVIEW user event is only created when a valid VI refnum is provided. The extension library returns an error if the user event does not exist, which effectively breaks any infinite loops.