* Size of #captive_image_iochannel. Empty files are rejected and therefore
* this value is always >0 after successful captive_init().
* Value is detected by captive_giochannel_size(captive_image_iochannel).
* Size of #captive_image_iochannel. Empty files are rejected and therefore
* this value is always >0 after successful captive_init().
* Value is detected by captive_giochannel_size(captive_image_iochannel).