momentValue undefined on period-matching count

Create SMA(10) and add 9 numbers, using nextValue(). Now the 10th value is added via momentValue(). Currently, this leads to undefined, which is also proven by code review.

The 10th added momentValue() must result in a "momentally" of the 10th next-value pendant. Only after the SMA (and other indicators) are lifted over their undefined states, incoming moment-values are suitable.