CryptoPkg: RuntimeCryptLib: support free(NULL)

The ISO C standard says about free(),

  If ptr is a null pointer, no action occurs.

This is not true of the RuntimeFreeMem() internal function. Therefore we
must not forward the argument of free() to RuntimeFreeMem() without
checking.

Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Qin Long <qin.long@intel.com>
Cc: Ting Ye <ting.ye@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Qin Long <qin.long@intel.com>

CryptoPkg/Library/BaseCryptLib/SysCall/RuntimeMemAllocation.c

@@ -434,5 +434,11 @@ void *realloc (void *ptr, size_t size)
 /* Deallocates or frees a memory block */
 void free (void *ptr)
 {
-  RuntimeFreeMem (ptr);
+  //
+  // In Standard C, free() handles a null pointer argument transparently. This
+  // is not true of RuntimeFreeMem() below, so protect it.
+  //
+  if (ptr != NULL) {
+    RuntimeFreeMem (ptr);
+  }
 }