In some circumstances singular files with numbers in their name (like
turntable-1080p.png) might be detected as a UDIM.

The root cause in this particular instance was because BKE_image_get_tile_info
believed this file to be a tiled texture and replaced the filename with
a tokenized version of it. However, later on, the code inside image_open_single
did not believe it was tiled because only 1 file was detected and our
tiled textures require at least 2. This discrepancy lead to the broken
filename situation.

This was a regression since rB180b66ae8a1f as that introduced the
tokenization changes.