Incompatibility between desync detection and sparse saving

[loganmc10]

Describe the bug
When you enable both desync detection and sparse saving, you will get cell not found!: frame xx

I have the desync check interval set to 60, but with sparse saving, there is not always a cell/save available for that frame.

To Reproduce
Steps to reproduce the behavior:

• Enable desync detection and sparse saving

Expected behavior
Desync detection should probably grab the latest available cell if one is not present for the desired frame?

Environment

• OS: Linux
• ggrs version: latest master
• Transport layer: matchbox

Additional context
Add any other context about the problem here.

[gschup]

thanks for reporting! can you please try #115 ?

Overall I don't recommend using sparse saving together with desync detection, since the detection will be quite sparse, but it should at least not crash.