We were still calculating the maximum number of rows correctly,
so the extra data was really extra and would get re-written to the
beginning of the subsequent file.
The only case in which this would lead to database issues is if the
very last file was lengthened incorrectly, and the "nrows" calculation
would therefore be wrong when the database was reopened. Still, even
in that case, it should just leave a small gap in the data, not cause
any errors.
This includes both client.stream_insert_numpy and
client.stream_insert_numpy_context(). The test code is based on
similar test code for client.stream_insert_context, so it should be
fairly complete.
