When NULL is given to lpApplicationName we enable Windows' "magical"
path interpretation logic, which makes Tor 0.4.x behave in the same way
as previous Tor versions did when it comes to executing binaries in
different system paths.
For more information about this have a look at the CreateProcessA()
documentation on MSDN -- especially the string interpretation example is
useful to understand this issue.
This bug was introduced in commit bfb94dd2ca.
See: https://bugs.torproject.org/29874
