Blank result when output filename is same as PDF

[rodrigobdz]

Describe the bug
GhostScript deleting content of original file if output filename is same as in original file.

To Reproduce
Steps to reproduce the behavior:

pdfoptim -o printer-manual.pdf printer-manual.pdf

Expected behavior
Output file is optimized version of input file.

Log

Filesize difference -98.55% ✂️
Optimized version of printer-manual.pdf saved as printer-manual.pdf 🎉
# printer-manual.pdf is now blank

Solution
Check arguments and stop script together with a warning if argument outputFile is identical to input filename.