Fix savegamename being improperly built

Fixes the weird savegame name path string issue. All happens in dehacked.c, which overwrites the default SRB2 save path. Facts:

1. timeattackname is the game mod name truncated to 64 chars, so this is safe to append to savegamename
2. When overwriting savegamename, the old code used strncpy(..., ..., strlen(timeattackname). This copies the whole of timeattackname, but NOT the null char
   • Therefore, if the previous savegamename was C:\Users\MarcoZ\SRB2\srb2sav%u.ssg, the new string becomes sugoiers\MarcoZ\SRB2\srb2sav%u.ssg. THIS IS THE FAILURE POINT!
3. When appending the %u.ssg piece, that's appended to the end of the OLD string
   • sugoiers\MarcoZ\SRB2\srb2sav%u.ssg%u.ssg
4. srb2home is appended to the beginning of this string, whether that's your default SRB2 dir or another folder.
   • C:\Users\MarcoZ\SRB2\sugoiers\MarcoZ\SRB2\srb2sav%u.ssg%u.ssg
5. The result save name:
   • C:\Users\MarcoZ\SRB2\sugoiers\MarcoZ\SRB2\srb2sav0.ssg10.ssg (don't know where the 10 comes from...)

This fix attacks step 2, where using strcpy() auto-adds the null char to the end of timeattackname. As timeattackname is 64 chars and hence shorter than savegamename, strcpy() is safe to use.

All works correctly after that point: savegamename is now merely sugoi, and the template is now C:\Users\MarcoZ\SRB2\sugoi%u.ssg

Tested with srb2home paths both in the default SRB2 dir and in another folder.