nonpareil error on empty FASTQ file

When running `nonpareil` on an emtpy file, I get the error:
```
Nonpareil v3.5.5
Fatal error:
Unexpected end of file while decompressing
 [      0.0] Fatal error: Unexpected end of file while decompressing
```
An empty file is still a valid FASTQ. Would it be possible to print a warning and exit nicely with all output files with `0` or `NA` (so that they are valid when plotting)?