"if (ftdm_array_len(spanparameters) == paramindex)" is still off-by-one,
we want to stop at "ftdm_array_len(spanparameters) - 1", before we overwrite
the last (= terminating, NULL) element.

NOTE: i'd prefer an "argc, argv"-style interface here
Signed-off-by: Stefan Knoblich <s.knoblich@axsentis.de>