MultiMC crashing when trying to show server list

[TheChilliPL]

Operating System

Linux

Description of bug

With specific instances, showing server list seems to fail

Logs seem to show:

...
    4.632 D Writing account list to file.
    4.634 D Saved account list to "accounts.json"
    4.635 D RefreshSchedule: Background account refresh succeeded
    8.460 D Component list save performed now for "Create: Perfect World"
terminate called after throwing an instance of 'std::out_of_range'
  what():  map::at
/usr/bin/multimc: line 23: 113901 Aborted                    (core dumped) ./MultiMC "$@"
chilli@chilli-pc ~ [SIGABRT]>

It seems to happen with an instance to which .minecraft was imported. The server list was empty. hexdump only shows 0a 00 00 00, which according to the unofficial NBT documentation on Minecraft Wiki seems to be an empty compound NBT tag with empty name.

Steps to reproduce

1. "Edit Instance" on an instance
2. Click servers tab on the left
   MultiMC crashes

Suspected cause

MultiMC might expect servers.dat to have a servers NBT tag. Seems like in some cases it might be a fully empty tag (like {} in JSON)

This issue is unique

• I have searched the issue tracker and did not find an issue describing my bug.