If a 1919 semi-auto is properly and safely setup, the trigger/sear engagement will be adjusted to where the gun cannot fire out of battery. Basically you can take varying size drill bits and place them between the barrel extension and trunnion to see the point where the trigger engages the sear and will release the firing pin when you pull the trigger (properly adjust head-space first before checking timing). If the trigger will release the firing pin when the space is larger than .120 inch (min .030) between the barrel extension and trunnion, then the gun can fire out of battery and would be dangerous if you were ever to pull the trigger when the bolt is traveling forward prior to when the bolt is in the last .120 inch of travel. From what I've seen, many 1919 semi manufacturers omit to make sure that their guns are timed properly in this regard. I suspect this is the cause of many of the out-of-battery explosions that sometimes are reported on this board.
If the gun is capable of firing out of battery, I would think that a crank fire mechanism would greatly increase the odds of this happening due to the fact it is able to pull the trigger much faster than normal when just using your finger. While not guaranteeing complete safety if the gun can fire out of battery, if just using your finger, you'll likely not be able to release the trigger and pull it again fast enough to trip the sear while the bolt is still in it's forward movement.