Many fonts make first start too long

[qubodup]

In the past, apparently each starting of Inkscape took ages if many fonts were installed. Nobody complained since 2015 so it's probably resolved https://bugs.launchpad.net/inkscape/+bug/488247

However, just like GIMP, Inkscape now appears to suffer from an extremely slow first start if many fonts are installed. In the case of the computer on which I'm experiencing it: 454 font sets in 1291 files. Windows 10 64bit.

What happens: inkscape starts (no window shows up, nothing is visible to end user but it is visible in the task manager) after about 7 minutes, the Inkscape window starts. If I then close inkscape and start it again, it starts in 2 seconds.

This is a border case but can be a problematic one. Education center computers are often configured to reset themselves after each restart, meaning each user who starts Inkscape after the computer had been restarted for the first time, will think Inkscape is not working if enough fonts are installed.

Problem 1: Inkscape is invisible while caching (?) fonts.

Problem 2: Caching (?) fonts takes possibly intolerably long.

Solution 1: Make the fact that fonts are being cached visible. Show a minimal window with a progress bar, percentage, current/total number display, estimated time to finish.

Solution 2: Add an "abort caching" button, which will abort caching the current font and start inkscape with only the fonts available that had been cached successfully.

[Patrick Storz (ede123)]

Duplicate of bug #1528629.