libwebp: Fix VP8EncTokenLoop() progress

Encoding the image found in the user bug report below would result in
a progress rising up to 173% because of the extra 20% caused by each
of the 4 extra lossy passes. It happened at methods 3 to 6.

https://groups.google.com/a/webmproject.org/g/webp-discuss/c/yOiP8APubgc/m/FP3r5X2rDAAJ

Change-Id: I95318d0dc4df546044eb926c786c04bb7f915cbe
(cherry picked from commit db25f1b4ed2ef519b6a3fd1d7ebfbcdfe2cc9712)
1 file changed