monitor: Fix invalid read

ERROR: AddressSanitizer: global-buffer-overflow on address 0x000000512c08 at pc 0x00000041848d bp 0x7ffcdde71870 sp 0x7ffcdde71860
READ of size 8 at 0x000000512c08 thread T0
    #0 0x41848c in print_attributes monitor/nlmon.c:6268
    #1 0x42ac53 in print_message monitor/nlmon.c:6544
    #2 0x438968 in nlmon_message monitor/nlmon.c:6698
    #3 0x43d5e4 in nlmon_receive monitor/nlmon.c:7658
    #4 0x4b3cd0 in io_callback ell/io.c:120
    #5 0x4b085a in l_main_iterate ell/main.c:478
    #6 0x4b0ee3 in l_main_run ell/main.c:525
    #7 0x4b0ee3 in l_main_run ell/main.c:507
    #8 0x4b13ac in l_main_run_with_signal ell/main.c:647
    #9 0x4072fe in main monitor/main.c:811

monitor/nlmon.c

@@ -5631,6 +5631,7 @@ static const struct attr_entry control_port_attr_table[] = {
 			"Interface Index", ATTR_U32 },
 	{ NL80211_ATTR_WIPHY,
 			"Wiphy", ATTR_U32 },
+	{ }
 };
 
 static const struct attr_entry scan_flag_table[] = {