FIX: short circuit parameters for calculations with 1 beta angle
FIX: short circuit parameters for calculations with 1 beta angle

The former code will fail due to an IndexError, if the calculation
was done with a default beta angle of 0°. Then the lists for
ld, lq and psim will have a length of 1.

The current code checks the length of these lists before accessing them.

SEMAFORInformatik/femagtools,SEMAFORInformatik/femagtools