Fix two bugs reported via Windows Crash Reporting:
* Freelance initialization is somehow broken allowing the number of
locally defined mountpoints to become negative. Due to the use of
!= instead of < in loops, it is possible to read/write unallocated
memory.
* GetTextualSid() was not properly handling a NULL output buffer
pointer as an indication that the desired size should be returned.
(cherry picked from commit 77de32ed745d912e35990c5602b4a69a1b654973)
0b95cfab6f