afs: Fix check for NULL terminator

Add a missing check for reaching the end of the string while attempting
to split a command.

Fixes: f94f70d ("afs: Provide a way to configure address priorities")
Reported-by: syzbot+7741f872f3c53385a2e2@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=7741f872f3c53385a2e2
Signed-off-by: Leo Stone <leocstone@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/4119428.1753108152@warthog.procyon.org.uk
Acked-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: leocstone

fs/afs/addr_prefs.c

@@ -48,7 +48,7 @@ static int afs_split_string(char **pbuf, char *strv[], unsigned int maxstrv)
 		strv[count++] = p;
 
 		/* Skip over word */
-		while (!isspace(*p))
+		while (!isspace(*p) && *p)
 			p++;
 		if (!*p)
 			break;