Fix memory leak and heap corruption on Windows.

LPSECURITY_ATTRIBUTES is type definition for pointer to SECURITY_ATTRIBUTES
structure.

Change-Id: I94a835bfd8f7eb76c808fac8286ca3f2db9b19c3
Reviewed-on: https://code.wireshark.org/review/4449
Reviewed-by: Michael Mann <mmann78@netscape.net>
Petri-Dish: Michael Mann <mmann78@netscape.net>
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>