properties: fix serialization of values

When the first parsed part of the value does not look like a container,
dump the complete length of the value.

If a value would contain 'Tunnel sink', it would previously only
serialize the 'Tunnel' part and ignore the rest.

See #3212

src/pipewire/properties.c

@@ -788,6 +788,9 @@ int pw_properties_serialize_dict(FILE *f, const struct spa_dict *dict, uint32_t
 		if ((len = spa_json_next(&sub, &value)) < 0)
 			break;
 
+		if (!spa_json_is_container(value, len))
+			len = value ? strlen(value) : 0;
+
 		dump(c, c->indent, &sub, value, len);
 		count++;
 	}