Do not convert 'symbolic-rtl' versions.

[madpilot78]

While updating the FreeBSD port I got failures due to cp failing to find some files, referenced by symlinks:

install -d /wrkdirs/usr/ports/x11-themes/xfce-icons-elementary/work/stage/usr/local/share/icons
cp -rf build/elementary-xfce /wrkdirs/usr/ports/x11-themes/xfce-icons-elementary/work/stage/usr/local/share/icons
cp: build/elementary-xfce/actions/24/go-previous-symbolic-rtl.png: No such file or directory
cp: build/elementary-xfce/actions/24/media-skip-forward-symbolic-rtl.png: No such file or directory
cp: build/elementary-xfce/actions/24/media-skip-backward-symbolic-rtl.png: No such file or directory
cp: build/elementary-xfce/actions/24/go-next-symbolic-rtl.png: No such file or directory
cp: build/elementary-xfce/actions/24/media-seek-forward-symbolic-rtl.png: No such file or directory
cp: build/elementary-xfce/actions/24/media-seek-backward-symbolic-rtl.png: No such file or directory
*** Error code 1

Looks like some finles with a new namiong scheme (*-symbolic-rtl.svn) have been added in commit 1c135ad but the expressions in the svgtopng/pngtheme.sh script have not been updated to account for this.

This is the fix I'm using in the FreeBSD ports tree.

[ochosi]

Looks good - thanks for the fix!