Fix Core Bug: To make "01/01/1970" a valid birthday

[1Shiroyuuki1]

When parsing "01/01/1970" as date to setDate() the output is '0'.
Because default value of strtoftime() is "01/01/1970".

    public function setDate($date)
    {
        $this->setTime($date ? strtotime($date) : false);
        $this->setData('date', $date);
        return $this;
    }

Description (*)

According to this bug means that Magento 1.X.X never allowed a birthday of "01/01/1970".
A simple null check in the getter will prevent it.

Manual testing scenarios (*)

1. https://www.tehplayground.com/auf4jhP1T5thJDtK
2. Text form:

<?php
// example code

//setDate() simulation
$customerBirthday = '01/01/1970';
$isDate             = $customerBirthday ? strtotime($customerBirthday) : false;

//getDate() simulation
$isDate ? print('Yeaj 01/01/1970 is valid') : print('but it´s not...');

//fix
($isDate !== null) ? print('Yeaj 01/01/1970 is valid') : print('but it´s not...');

?>

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All automated tests passed successfully (all builds are green)
• [Having Issues] Add yourself to contributors list

[kiatng]

I tested setting the dob to 01/01/1970 in both frontend and backend. Actually, the dob is set correctly in both cases. However, in frontend, the dob was empty even though its value is 01/01/1970. This PR fixes it.

[1Shiroyuuki1]

Is it possible to merge this as asap ? , i´ve got another core bug which would result on this issue and a fix as well

[1Shiroyuuki1]

I have fixed a following bug after this fix.
@kiatng strtotime returns via default a value of "01/01/1970". If you create a new customer and leave birthday input empty you will get this value as default birthday.

Steps to Reproduce:
(Frontend)

1. Create a new Customer
2. Leave Birthday input Empty
3. Save
4. Try to edit this customer again and you will see the default value of strtotime()

Fix: I have improved the settime() and getTime() method and replaced strtotime with a Datetime. There is absolutely no reason to parse a unix timestamp for a birthday date.
Since strtotime was very often used in php 4.x.x i think adobe never cares to improve their Date handling.
With us now supporting PHP 7++ we should consider to clean up this as well.

Awaiting new Review :)

[kiatng]

@1Shiroyuuki1 I tested your commit and it worked as expected. One last request from me:

magento-lts/app/code/core/Mage/Customer/Block/Widget/Dob.php

Line 28 in c48b366

* @method string getTime()

The docblock needs to be updated:

  * @method DateTime getTime() 

Please do another commit.

[1Shiroyuuki1]

@kiatng done 👍

[github-actions]

Unit Test Results

1 files  ±0  1 suites  ±0   0s ⏱️ ±0s
0 tests ±0  0 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
7 runs  ±0  5 ✔️ ±0  2 💤 ±0  0 ❌ ±0 

Results for commit dacba02. ± Comparison against base commit 3ef5922.