Avoid accessing out of bounds elements

When pruned == false and currCnt == MAX_NUM_HMVP_CANDS,
memmove() copied element motionCand[MAX_NUM_HMVP_CANDS] which is
out of bounds. With this fix one fewer elements is copied.
The element that was previously incorrectly copied was overwritten
by memcpy(). Hence there is no change in the result.
See also #113