Fix (unreported) buffer overflow in BLI_system_cpu_brand_string helper.

Since this buffer is used as an array of 12 32bits integers, and C++
string expect a NULL-terminated C-string, we need an extra char to
ensure last one is always NULL.

See D8906. Thanks to @brecht for noting this one too.

source/blender/blenlib/intern/system.c

@@ -135,7 +135,7 @@ static void __cpuid(
 
 char *BLI_cpu_brand_string(void)
 {
-  char buf[48] = {0};
+  char buf[49] = {0};
   int result[4] = {0};
   __cpuid(result, 0x80000000);
   if (result[0] >= (int)0x80000004) {