StdLib/LibC/StdLib/Malloc.c: Make the free() function conform to the ISO/IEC 9899...

StdLib/LibC/StdLib/Malloc.c:  Make the free() function conform to the ISO/IEC 9899 (C95) specification.

The C95 specification states: "The free function causes the space pointed to by ptr to be deallocated, that is, made available for further allocation.  If ptr is a null pointer, no action occurs".  The UEFI FreePool() function, which the StdLib implementation of free() uses, does not make this check.  This fix adds a check for null to the free() function such that if the pointer argument is NULL, nothing is done.

Contributed-under: TianoCore Contribution Agreement 1.0
Reviewed-by: erik.c.bjorge@intel.com
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@13739 6f19259b-4bc3-4df7-8a09-765794883524