[wp-trac] [WordPress Trac] #37508: wpdb->result instance should be checked `mysqli_num_fields` in `load_col_info()`

[WordPress Trac]

#37508: wpdb->result instance should be checked `mysqli_num_fields` in
`load_col_info()`
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 Reporter:  giuseppe.mazzapica  |      Owner:
     Type:  defect (bug)        |     Status:  new
 Priority:  normal              |  Milestone:  Awaiting Review
Component:  Database            |    Version:  trunk
 Severity:  normal              |   Keywords:
  Focuses:                      |
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 In `wpdb::load_col_info()` the function `mysqli_num_fields()` is called
 passing `$this->result` without any check on this property value.

 The problem is that function has a type hint to `mysqli_result` (see
 http://php.net/manual/en/mysqli-result.field-count.php), but
 `$this->result` may be `false`.

 Just like in other places in the same class, the function should check
 that `$this->result instanceof mysqli_result` before calling
 `mysqli_num_fields()`.

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Ticket URL: <https://core.trac.wordpress.org/ticket/37508>
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