C: False positive about "Potential double free" with negative array indices

**Description of the false positive**

CodeQL warns about potential double free, in situations where there's clearly no such situation. It seems to be related to the use of negative indices

**Code samples or links to source code**

Cf https://github.com/MapServer/MapServer/security/code-scanning/3

The code at https://github.com/MapServer/MapServer/blob/0cb56232d4ca0e64d747efa1db602ff08e0ea42f/src/mapparser.c#L1787 (which is C code generated from a Bison grammar)
```
free((yyvsp[-2].strval));
free((yyvsp[0].strval));
```

generates "Memory pointed to by may already have been freed by. ", but this is obviously wrong as the memory locations are disjoint.

Extract of "Show path" in the report:
```
Step 1 pointer to free output argument
Source
src/mapparser.c:1787
}
}

free((yyvsp[-2].strval));
free((yyvsp[0].strval));
}
#line 1791 "/vagrant/mapparser.c" /* yacc.c:1646 */
Step 2 *access to array [post update] [YYSTYPE]
src/mapparser.c:1787
}
}

free((yyvsp[-2].strval));
free((yyvsp[0].strval));
}
#line 1791 "/vagrant/mapparser.c" /* yacc.c:1646 */
Step 3 *access to array [YYSTYPE]
src/mapparser.c:1788
}

free((yyvsp[-2].strval));
free((yyvsp[0].strval));
}
#line 1791 "/vagrant/mapparser.c" /* yacc.c:1646 */
break;
Step 4 strval
Sink
src/mapparser.c:1788
}

free((yyvsp[-2].strval));
free((yyvsp[0].strval));
Memory pointed to by
may already have been freed by
.
}
#line 1791 "/vagrant/mapparser.c" /* yacc.c:1646 */
break;
```

Start by reviewing the MapServer example at src/mapparser.c:1787 and the linked code-scanning report, focusing on the two frees using negative and zero indices. Then trace the relevant CodeQL query and its handling of array accesses. Done means the query no longer reports this disjoint-memory case while preserving genuine double-free findings.

Escrita pelo modelo de indexação a partir do texto da issue.