EmulatorPkg/PosixFileSystem: Add NULL check on memory allocation
REF: https://bugzilla.tianocore.org/show_bug.cgi?id=4001
This commit adds NULL check on memory allocation of the size
for FileName in ASCII string format at PosixFileSetInfo().
Signed-off-by: Miki Shindo <miki.shindo@intel.com>
Cc: Andrew Fish <afish@apple.com>
Reviewed-by: Ray Ni <ray.ni@intel.com>