Yes, you are missing the door check. If you can't locate one through a vendor you should be able to get a used one. The door check is very useful and worth the effort to find one.
Just to clarify the purpose of the door check is to keep the door from swinging too far open and denting the sheet metal or cowl area in front of it.
On the door hinges you will find what are called Spring Detent Plates. One set holds the door fully open the other set half open they come in right and left and upper and lower hinge kits. I don't know if they are available for 1948 vehicles? On a 41 these can only be installed with the hinge off the car and they are riveted in place. I have 4 extra hinge sets and all have the spring detent plates broken. Working on the hinges will necessitate removing the door. While most can find a way to remove a door few will have the skill and patience to reinstall it and align it correctly. I recommend tackling door projects only after memorizing the manual and as part of body restoration.
I have pictures and a video to get most through the project but caution the few "brave and the strong," who take on the project. Having a body shop door hanger would be the ultimate aide, I used an engine hoist with a load leveler.