AGI: Animation and timers too fast with OpenGL backend

[dmwarren]

Game
KQ1 AGI from the Roberta Williams Anthology. ScummVM identifies it as v2.0F 1987-05-05 5.25"/3.5"/DOS/English

logdir: 10ad66e2ecbd66951534a50aedcd0128
vol.0: 9081ab588c09202729cfd224b2f57301
object: 6eca02fa540337308529ff13e9e764aa

Also reproducible with Fastest mode in The Black Cauldron (2.00 1987-06-14 DOS/English), freely available at ​http://allowe.com/downloads/games.html

Platform
OS X 10.11.6

Problem
Setting the animation speed to "fast" or "fastest" makes the animation run at an almost unplayably fast speed.

Timers run fast as well. (e.g., in KQ1 the fairy dust only lasts ~40 seconds)

Was not able to reproduce bug with other graphics backends or other AGI titles (KQ2, KQ3, SQ2).

Last commit where bug was not present
778c1ddb69bb45b6992fdc9b8fff6b2c8d3e22ac

First commit where bug is present
34117170f2955e854a93925a652af37575361b44

Steps to Reproduce

1. Grab OS X machine. (haven't tested other platforms)

2. Load KQ1 (see version info above) or The Black Cauldron with an affected version of ScummVM.

3. Set Graphics mode to OpenGL, either filtered or unfiltered.

4. Start game. Switch to 'fast' or 'fastest' animation speed.

5. Move around. If the bug is present, it will take just ~4 seconds to cross a screen. Fine movement will be very difficult because you're moving too fast. Timers will expire in seconds instead of minutes.