Fix saving plain webvfx resource with absolute path.
Fix saving plain webvfx resource with absolute path.

Regression in previous commit 06c0662.
Fixes Shotcut bug https://github.com/mltframework/shotcut/issues/225

siddharudh/mlt,siddharudh/mlt,j-b-m/mlt,j-b-m/mlt,siddharudh/mlt,mltframework/mlt,j-b-m/mlt,mltframework/mlt,mltframework/mlt,siddharudh/mlt,xzhavilla/mlt,j-b-m/mlt,siddharudh/mlt,mltframework/mlt,xzhavilla/mlt,mltframework/mlt,xzhavilla/mlt,siddharudh/mlt,mltframework/mlt,xzhavilla/mlt,siddharudh/mlt,j-b-m/mlt,mltframework/mlt,mltframework/mlt,mltframework/mlt,xzhavilla/mlt,xzhavilla/mlt,siddharudh/mlt,j-b-m/mlt,xzhavilla/mlt,j-b-m/mlt,xzhavilla/mlt,j-b-m/mlt,mltframework/mlt,j-b-m/mlt,siddharudh/mlt,j-b-m/mlt,xzhavilla/mlt