[5.3] Improve error handling for creating autload_psr4.php

[Hackwar]

Summary of Changes

This PR stems from an update issue. After updating, the /administrator/cache/autoload_psr4.php is deleted and should be regenerated automatically. However the webspace was full and thus the file couldn't be written. In theory we have a fallback for this, however that fallback expects an exception to be thrown, which the code actually doesn't do. This PR adds an additional check for this.

Unfortunately I couldn't replicate the issue itself, since I can't make the folder write-protected on my windows machine and I don't have a Linux machine available right now to test this. So this change was done by me on codereview alone.

Testing Instructions

1. Delete /administrator/cache/autoload_psr4.php
2. Make the /administrator/cache folder unwritable
3. Open the site.

Actual result BEFORE applying this Pull Request

The site displays a 500 error about being unable to include the autoload_psr4.php and the file is not created.

Expected result AFTER applying this Pull Request

The site works like before, even though it might be a bit slower. The autoload_psr4.php is not created.

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[joomdonation]

I have tested this item ✅ successfully on 67e4d51

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/44763.}

[viocassel]

I have tested this item ✅ successfully on 67e4d51

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/44763.}

[QuyTon]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/44763.}

[pe7er]

I also tested this PR successfully with the permissions on the cache folder set to unwritable (so chmod 500, with only read + execute permission). Site with this PR works without the /administrator/cache/autoload_psr4.php in place.

[pe7er]

Thanks @Hackwar !