`runtime/lib/util/BasePeer.php:500-503` gives warnings in PHP7.4

[nicolasderouet]

PHP Deprecated: Array and string offset access syntax with curly braces is deprecated

Fix: runtime/lib/util/BasePeer.php line 399 to 405
From:

for ($r = 0, $len = strlen($raw); $r < $len; $r++) {
  if ($raw{$r} == '?') {
    $rawcvt .= ':p' . $p++;
  } else {
    $rawcvt .= $raw{$r};
  }
}

To:

for ($r = 0, $len = strlen($raw); $r < $len; $r++) {
  if ($raw[$r] == '?') {
    $rawcvt .= ':p' . $p++;
  } else {
    $rawcvt .= $raw[$r];
  }
}

[DavidGoodwin]

see also #1082