Output file silently truncated when not enough space is available

[jspam]

Thank you very much for this tool (and your work on -ftime-trace)!

I tested it on our medium-sized project, where --stop creates a 3.8GB output file. I did not have enough free space in the output folder (as I later realized). However, the --stop command succeeded (exit code 0) and did not give an error message. Only when --analyze failed to parse the JSON file I realized the output had been truncated.

Other file writing errors are detected, such as missing write permissions.