Fix: Do not pass null to function that expects DateTime or string

[localheinz]

This pull request

• stops passing null to a function that expects DateTime or string

Follows #847.

💁‍♂️ Running

git grep -i format_interval

on current master yields

eol.php:51:				<?php $eolPeriod = format_interval($eolDate, null) ?>
include/branches.inc:46:function format_interval($from, $to) {
supported-versions.php:66:					<td class="collapse-phone"><em><?php echo htmlspecialchars(format_interval($initial, null)) ?></em></td>
supported-versions.php:68:					<td class="collapse-phone"><em><?php echo htmlspecialchars(format_interval($until, null)) ?></em></td>
supported-versions.php:70:					<td class="collapse-phone"><em><?php echo htmlspecialchars(format_interval($eol, null)) ?></em></td>

Before

See http://localhost:8080/supported-versions.php:

After

See http://localhost:8080/supported-versions.php:

[localheinz]

Alternatively, we could create $to in the function, but that would make it harder to test if we wanted to test it.

[localheinz]

Thank you, @kamil-tekiela!