Treat a zero GIF delay as 100ms

A GIF frame delay under 20ms means "as fast as possible", and browsers clamp
it to 100ms - the speed the emote actually plays at where people see it.
Summed literally, :Awkward: reported 76 frames lasting 0.1s and collapsed to
a single still. Any emote authored that way would have silently become a
static image.

tools/add_emote.py

@@ -84,6 +84,11 @@ def load_frames(blob):
         fitted.paste(scaled, ((cw - scaled.width) // 2, (ch - scaled.height) // 2))
         frames.append(fitted)
         durations.append(page.info.get('duration') or 0)
+    # A GIF delay under 20ms means "as fast as possible"; browsers clamp it to
+    # 100ms, so that is the speed the emote actually plays at where people see
+    # it. Taken literally, a sheet of zero-delay frames looks like a 0-second
+    # animation and collapses to one frame.
+    durations = [d if d >= 20 else 100 for d in durations]
     return frames, durations, (cw, ch)