FILE_CACHE_MAX was meant to be larger than FILE_MAX to make room
for additional layers in the path. An error in the define used
`FILE_MAXFILE + FILE_MAXFILE` instead of `FILE_MAXDIR + FILE_MAXFILE`
causing the value to be smaller allowing a buffer overflow when passing
the string into BLI_path_abs.
Correct the define and call on the directory component before
the file is added so it doesn't clamp the string length unnecessarily.
Note that some values weren't correct since the original commit [0],
although [1] moved them to a shared incorrect define.
[0]: 78cdc707ab
[1]: cef1b9c30f
2a892012be