Ref T13216. See PHI948. When you use the remarkup hint button to embed a meme with no text, you get {meme src=X}.
If the source is a GIF, we currently split the source apart into frame-by-frame images, process them, and stitch them back together. The end result is the same image we started with, but this process can be slow/expensive, and may timeout for sufficiently large GIFs.
Instead: when there's no text, just return the original image data.