fix crash on th095 when score length is less than 3

[Ltfjx]

If scoreString's length is less than 3, insertPosition will become a negative number, which is not allowed by size_t and will cause std::out_of_range exceptions.

Same problem but has fixed in createFormattedScore()

[TheBakaRem]

…woops, I didn't know that was an issue.
I was told that th095 had a main menu crash two weeks ago, and this is probably what caused it. Didn't catch it either when testing, since my savefile didn't have an empty score (which I think would be the only way for someone to have a score string of less than 3 characters).
I'll have to review the rest of the code to see if I didn't do the same error elsewhere, which is a possibility.

Thanks for the PR and sorry for the delay!