src/acpi/acpigen: Add NULL pointer check

Add NULL pointer check in acpigen_emit_namestring
to avoid segmentation fault.

Change-Id: I3d01d28e74f202278b5a5a96d2edd45c66f10883
Signed-off-by: Ronak Kanabar <ronak.kanabar@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48148
Reviewed-by: Subrata Banik <subrata.banik@intel.com>
Reviewed-by: Maulik V Vaghela <maulik.v.vaghela@intel.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/acpi/acpigen.c

@@ -291,6 +291,10 @@ void acpigen_emit_namestring(const char *namepath)
 	int dotcount = 0, i;
 	int dotpos = 0;
 
+	/* Check for NULL pointer */
+	if (!namepath)
+		return;
+
 	/* We can start with a '\'. */
 	if (namepath[0] == '\\') {
 		acpigen_emit_byte('\\');