fix: Integer underflow in lexer error message formatting

[hkrutzer]

See #518

The example now produces:

Error adding policy:
--> example.rego:8:0
  |
8 | match("^hello", text)
  | ^
error: invalid whitespace between . and identifier
Input set successfully
Result: QueryResults {
    result: [],
}

fixes #518

[Anand Krishnamoorthi (anakrish)]

Hey hkrutzer, Thanks for the fix. Can you also add an interpreter test here to lock down the scenario:

regorus/tests/interpreter/cases/call/basic.yaml

Line 78 in d4b7d1f

[hkrutzer]

Added!

@microsoft-github-policy-service agree

[Anand Krishnamoorthi (anakrish)]

LGTM. Thanks for the fix, hkrutzer.