Fix error on negative counts with no function_name.

[wsnyder]

This fixes a crash with negative counts. Also fixes some extraneous trailing spaces.

The backtrace this solved is as follows:

Process Process-1:
Traceback (most recent call last):
  File "/usr/lib/python3.10/multiprocessing/process.py", line 314, in _bootstrap
    self.run()
  File "/usr/lib/python3.10/multiprocessing/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "/.../fastcov.py", line 335, in gcovWorker
    distillSource(f, base_report["sources"], args.test_name, args.xbranchcoverage)
  File "/.../fastcov.py", line 714, in distillSource
    distillLine(line, sources[source_name][test_name]["lines"], sources[source_name][test_name]["branches"], include_exceptional_branches)
  File "/.../fastcov.py", line 677, in distillLine
    logging.warning("Ignoring negative count found in %s.", line_raw["function_name"])
KeyError: 'function_name'

[RPGillespie6]

Nice catch, thanks for the fix.