[physfs] PHYSFS_setWriteDir creates an empty file if the path its given does not exist

[Ryan C. Gordon]

> My question is: Is this a regression/bug in physfs 3.0.1 or is it a
> feature now? If it is the latter I would appreciate some comments how to
> fix this issue in lincity-ng with physfs 3.0.1.

This is a regression; I've pushed a fix here:

https://hg.icculus.org/icculus/physfs/rev/a29fef4a20fd

And will be rolling a 3.0.2 shortly, once I sort out some other issues.

--ryan.