BUG: Handling of extrafield type "date" not correct

[glu000]

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Bug

handling of extrafield date is not correct in function insertExtraFields.

Environment

• Version: 9.0
• OS: n/a
• Web server: n/a
• PHP: n/a
• Database: n/a
• URL(s): n/a

Expected and actual behavior

Wrong data is stored, when a date is entered in any form into an extrafield-type "date"

Steps to reproduce the behavior

1. Create an extrafield with type "date" (e.g. in proposal)
2. Enter a date in a new proposal into this extrafield -> wrong data is stored

Suggested implementation

File: core/class/commonobject.class.php
Function: insertExtraFields, line 5027
-> handle extrafield date in the same way than extrafield datetime

if (! is_int($this->array_options[$key])) {
	$this->array_options[$key] = strtotime($this->array_options[$key]);
}