[BUG] fileio add_mapping allows invalid physical path

[dedmen]

Describe the bug


code uses size + 1 (+1 for the ending slash) and thus expects that phys path doesn't have endling slash.
but add_mapping doesn't verify/fix that if you do
add_mapping("T:/", "/")
it keeps the ending slash, which makes this code in screenshot trim one character too many.

so tree->physical now has "T:/" entry, but should just be "T:"

To Reproduce
Steps to reproduce the behavior:

1. Make pdrive
   2, add_mapping("P:/", "/")
2. try to compile P:/a3/functions_f_enoch/em_core/fn_showspectrumanalyzer.sqf
3. include not found error for #include "define.inc"

Expected behavior
add_mapping should verify/remove trailing slash on physical path.
or get_info_physical should assume that folder path always ends with trailing slash, and add_mapping should also be adjusted for that,