Correctly append a suffix to the mangled temporary file name

Correctly append a suffix to the mangled temporary file name

When two users end up with the same mangled temporary file name, a suffix is
supposed to be added at the end of the new file name to make it distinct from the
previous one but the suffix was added one byte too far making it useless.

The result was that the log entries of two or more users were written into the
same file overwritting each other's data and corrupting the report.

Thanks to Mark Dennison for reporting this bug.