Always call ConvertToI420 with positive crop_height

Source height may be negative, causing libyuv to invert the image.
However the height of the destination buffer specified by crop_height
should be positive. Remaining calls in common_video_unittests are valid.

Bug: webrtc:9447
Change-Id: I6d398909ae80a99d228ccbbd8c1d7ae804e5bf8d
Reviewed-on: https://webrtc-review.googlesource.com/c/86540
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Per Kjellander <perkj@webrtc.org>
Reviewed-by: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25427}
diff --git a/AUTHORS b/AUTHORS
index c85a4e8..1804f5f 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -48,6 +48,7 @@
 Rafael Lopez Diez <rafalopezdiez@gmail.com>
 Ralph Giles <giles@ghostscript.com>
 Riku Voipio <riku.voipio@linaro.org>
+Robert Bares <robert@bares.me>
 Robert Nagy <robert.nagy@gmail.com>
 Ryan Yoakum <ryoakum@skobalt.com>
 Satender Saroha <ssaroha@yahoo.com>