Open idx/sub file with one image causes lockup

[felf]

I'm working on a series of episodes. The forced track often has just one line of text: the translation of the title card. For some episodes it works, for others it doesn't. If not, then the preview window opens, but the program hangs up while constructing the window's widgets.

Maybe the sub file is invalid, as it does not contain much besides 0x00 and 0xFF and is only half as big. But in that case maybe the program should catch that and give an error message instead of baulking. I attached a working and broken version of such a subtitle for reproducability.

I use 4.0.10 on Arch with wine.

subfiles.zip