blspec: Do not crash on config files without newline on last line

When the last line in a config file has no newline then 'next' is NULL
on the the loop iteration. Check that before derefencing 'next'.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

common/blspec.c

@@ -75,7 +75,7 @@ static struct blspec_entry *blspec_entry_open(struct blspec *blspec,
 
 	next = buf;
 
-	while (*next) {
+	while (next && *next) {
 		char *name, *val;
 
 		line = next;