The handling of N-to-M array compression was broken with the addition
of the partial buffer option, which broke the bounds check that was
being used.
Note that this also makes the partial buffer option more consistent;
if, for example, you have
```
record(compress, foo) {
field(ALG, "N to 1 Average")
field(INP, "bar NPP")
field(NSAM, 2)
field(N, 2)
field(PBUF, YES)
}
```
(with `bar` having, e.g. length 3), then this will now behave as
expected on both of the samples.
beec00b403