Bloaty accepts `-n 0` but not `max_rows_per_level: 0` when using `-c` option

[Kendal Harland]

Title is self explanatory. When bloaty is given max_rows_per_level: 0 via bloaty -c bloaty.textproto file it errors with:

bloaty: max_rows_per_level must be at least 1

However, specifying bloaty -n 0 on the command line does the right thing as expected.