invalid characters in flame name cause render crash

[foundation]

Had a flame accidentally named with a \ at the end "Apophysis-101128-38~4\" (no quotes) and when I was rendering all the flames with flam4, it had an error upon hitting that one and I had to restart fr0st. I assume it was because of the invalid file system character in the name (I had accidentally typed that while saving in apophysis) the same flame is rendering fine right now without the slash. I haven't yet tested whether this affects flam3 renderer also.

[Vitor Bosshard (algorias)]

Confirmed to affect windows only.