D-Bus: Allow empty string in dbus network properties

This is needed for clearing previously set parameters in a similar
manner that was already available through the control interface
SET_NETWORK command.

Signed-off-by: Matthew Wang <matthewmwang@chromium.org>

wpa_supplicant/dbus/dbus_new_handlers.c

@@ -230,8 +230,6 @@ dbus_bool_t set_network_properties(struct wpa_supplicant *wpa_s,
 		} else if (entry.type == DBUS_TYPE_STRING) {
 			if (should_quote_opt(entry.key)) {
 				size = os_strlen(entry.str_value);
-				if (size == 0)
-					goto error;
 
 				size += 3;
 				value = os_zalloc(size);