Description:
------------
When making a variable global inside a function and using it as an index to access a SimpleXML element, the variable's value is non-properly handled and the XML's element is not returned (although you can error_log the variable's value and type).

If you cast the variable to an integer, the XML's element is returned (as expected) - see column #2.

Compare the results of the four different tests in the sample script.

Also:
- if you try the test removing the function call (to avoid declaring the variable as global), the expected element is returned.

- using $GLOBALS also works returning the expected element.

- the output of the code is different between PHP 5.4.16 and PHP 7.0.8

Test script:
---------------
<?php

$tpnb = 5;

test();
die();

function test() {

    global $tpnb;

    error_log('$tpnb value: ' . $tpnb . ' type:' . gettype($tpnb));

    $xmlStruct = <<<EOF
<?xml version="1.0" encoding="UTF-8"?>
<templates>
    <object type="obj_1" label="Label for object 1"></object>
    <object type="obj_2" label="Label for object 2"></object>
    <object type="obj_3" label="Label for object 3"></object>
    <object type="obj_4" label="Label for object 4"></object>
    <object type="obj_5" label="Label for object 5"></object>
    <object type="obj_6" label="Label for object 6"></object>
    <object type="obj_7" label="Label for object 7"></object>
    <object type="obj_8" label="Label for object 8"></object>
    <object type="obj_9" label="Label for object 9"></object>
    <object type="obj_10" label="Label for object 10"></object>
</templates>
EOF;
    $tplxml = simplexml_load_string($xmlStruct);

    echo '<table border="1">';
    echo '<tr>';

    echo'<td style="vertical-align:top"><pre><h1>1: $tpnb</h1>';
    // try accessing "object" directly
    print_r($tplxml->object[$tpnb]);
    echo '</pre></td>';

    echo'<td style="vertical-align:top"><pre><h1>2: (int) $tpnb</h1>';
    // try accessing "object" with an index cast
    print_r($tplxml->object[(int) $tpnb]);
    echo '</pre></td>';

    echo'<td style="vertical-align:top"><pre><h1>3: ($tpnb + 1 - 1)</h1>';

    // try accessing "object" by increasing and decreasing the index
    print_r($tplxml->object[($tpnb + 1 - 1)]);
    echo '</pre></td>';

    echo'<td style="vertical-align:top"><pre><h1>4: temp var</h1>';
    // use a temporary variable to re-set the index in the same variable
    $tpnbx = $tpnb;
    unset($tpnb);
    $tpnb = $tpnbx;
    print_r($tplxml->object[$tpnb]);
    echo '</pre></td>';

    echo '</tr></table>';
}


Expected result:
----------------
All the columns should return:

SimpleXMLElement Object
(
    [@attributes] => Array
        (
            [type] => obj_6
            [label] => Label for object 6
        )

)

Actual result:
--------------
Column one is empty.