Essential dynamics: move bNeedDoEdsam evaluation to separate function

The bool variable edi->bNeedDoEdsam is used to signal whether any essential
dynamics constraints have to be evaluated for the ED group. This variable
was evaluated at the beginning of an ED simulation in write_edo_legend().
The latter is however not called if continuing from checkpoint. To
get rid of having to remember whether edi->bNeedDoEdsam was already
initialized, there is now a function bNeedDoEdsam(edi) that is evaluated
every time when called.
Also corrected a few typos.

Change-Id: Iab899a677a85ee8270354859c98cc9e5a9db34b7