Spaces in file names

Nobody has claimed this yet.

If the directory from which the program is started contains a space, dot won't be able to render the svg output: `pytest --profile --profile-svg` yields:

```
rror: dot: can't open with
Error: dot: can't open a space/prof/combined.svg
Traceback (most recent call last):
File "/usr/local/Cellar/python@3.9/3.9.0_5/Frameworks/Python.framework/Versions/3.9/bin/gprof2dot", line 8, in
sys.exit(main())
File "/usr/local/lib/python3.9/site-packages/gprof2dot.py", line 3457, in main
parser = Format(*args)
File "/usr/local/lib/python3.9/site-packages/gprof2dot.py", line 2685, in __init__
self.stats = pstats.Stats(*filename)
File "/usr/local/Cellar/python@3.9/3.9.0_5/Frameworks/Python.framework/Versions/3.9/lib/python3.9/pstats.py", line 114, in __init__
self.init(arg)
File "/usr/local/Cellar/python@3.9/3.9.0_5/Frameworks/Python.framework/Versions/3.9/lib/python3.9/pstats.py", line 128, in init
self.load_stats(arg)
File "/usr/local/Cellar/python@3.9/3.9.0_5/Frameworks/Python.framework/Versions/3.9/lib/python3.9/pstats.py", line 141, in load_stats
with open(arg, 'rb') as f:
FileNotFoundError: [Errno 2] No such file or directory: '/Users/.../path with a space'
```
This is with platform darwin -- Python 3.9.0, pytest-6.2.5, py-1.10.0, pluggy-1.0.0, plugins: profiling-1.7.0, lazy-fixture-0.6.3.

Reproduce the failure by running `pytest --profile --profile-svg` from a directory whose path contains a space on macOS with Python 3.9. Start by tracing how the profiling plugin invokes dot and passes output paths. Done means the command renders the SVG successfully when the working directory contains spaces, with coverage for that path-handling case.

Written by the indexing model from the issue text.