It is perfectly safe to self-dispatch a 3 car train, with 6 doors, all automatic, on a platform with a curve, irrespective of platform obstructions. It happens regularly, and I can think of a number of locations where I have to do it.
You just need to be aware of you surroundings and pay attention, and follow the correct the dispatch procedure.
I.e. - a) Observe that there are no obstructions and close doors.
b) Observe doors closing as far as practicable.
c) Observe orange door light extinguished on each carriage, whilst also checking again for obstructions. Moving position away from the train for a better line of sight if needed.
c) is the key one and, whilst not apportioning any blame, I would assume that no matter how curved the platform, during this part of the process the Guard would have noticed that there was an obstruction in the doors.
Railway Rule Book said:
3.6 Dispatching a train with
power-operated doors with a guard
from an unstaffed platform
You must first make sure all passengers are clear of the train doors.
You may then close the train doors.
If the driver operates the doors, you must give the close doors
signal to the driver.
[Driver-When you receive the close doors signal, you must close the
doors then acknowledge the close doors signal.]
When the doors are closed, you must carry out the train safety
check.
If it safe for the train to start, you must then:
where appropriate, close the local door
where appropriate, check the door interlock light is illuminated
give the ready-to-start signal to the driver
stay at the door controls until the train has passed clear of the
platform.
3.2 The train safety check
When the train doors have been closed (and on trains fitted with
central door locking, the central door locking has been locked), you
must carry out the train safety check by making sure that:
the train doors are properly closed
nobody is trapped in the doors, for example by clothing
it is safe to start the train.
You must do this by positioning yourself on the platform, if
necessary with another member of platform staff, so that the full
length of the train can be seen.
You must also check that the exterior hazard lights have gone out
on trains fitted with central door locking.
[Guard - You must carry out the train safety check if there are no platform
staff.]
Whilst I don't know the location concerned, with 3 coach train the train safety check should be perfectly easy to carry out without the need for additional platform staff, even with a curved platform.