Fix an exception on wx-3.0-gtk3 in PLCOpenEditor when generating ST files.

On Python2.7 with WX3.0 and GTK3, an assertionError rises on generating a ST file if the name is already set. The first generation works without problems, if you generate the file a second one, PLCOpenEditor tries to open the file
save dialog with the pre entered name from last run. Then the following assertion pops up:

PyAssertionError: C++ assertion "volDummy.empty() && pathDummy.empty()" failed at ./src/common/filename.cpp(568) in Assign(): the file name shouldn't contain the path

This fix reduces the filepath of the ST file the to the filename. Now it works fine.

#!/bin/bash

INKSCAPE=inkscape

for i in `cat icons.svg |grep -o -e '%%[^%]*%%'|sed 's/%//g'` 
do
 if [ $i.png -nt icons.svg ]; then
 	echo "Skip $i"
 else
	rm  -f $i.png
	echo "$INKSCAPE" icons.svg -z -e $i.png -i $i
	"$INKSCAPE" icons.svg -z -e $i.png -i $i
 fi
done