[REF] simplify CRM_Activity_BAO_Activity function by using early returns.

[REF] simplify CRM_Activity_BAO_Activity function by using early returns.

This function returns a bool. In the process it sets the  variable, however, once set to false in two places
it can never be set to true, so I am simply replacing a big if block with an early return to simplify the code.

This is a further block that can go but it is a slightly different patter & would remove 2 levels of 'if'
so it feels like an easier review if I leave that out of scope