Re-working checkRange to make take into account thieving boost

[marmadukeG]

Fixes #1273:

Thieving currently has a static max boost of "3", reworking checkRange to be more dynamic.

[pajlada]

Small nitpick for the formatting of the solution, otherwise I think this is a good solution for the problem 👍

You could format the code slightly different to make it a little bit more clear what it does, like this:

if (...boosts...) {
  ...
}
else if (skill == THIEVING) {
  if (real thieving level < 65) {
    highestBoost = 2;
  } else if (real thieving level < 45) {
    highestBoost = 1;
  }
}

Then run IntelliJ's formatter on your new code to align it properly

You can add the text: "Fixes #1273 " in the PR description, that way the issue will automatically close when this PR is merged in!