[KB-41052] Avoid error in CKEditor 4 with saveMode = base64

[xripoll-at-wiris]

Description

A customer reported that in CKEditor 4, when setting wiriseditorsavemode = base64 (instead of the default xml), the editor throws an error when double clicking a formula, and this lead to inconsistent behaviors. Among others, formulas would randomly disappear.

This was caused by the fix of KB-34325 introduced a few months ago, which would decode the src of base64 formulas, causing the Image#fixAfterResize function of the devkit to throw an error upon unexpectedly finding a formula NOT in base64 despite wiriseditorsavemode being set to base64.

Steps to reproduce

• Start the CKEditor 4 plugins demo for PHP, with this branch for html-integrations.
• Modify the configuration.ini file to have wiriseditorsavemode = base64.
• Check that you can correctly edit formulas, and no errors are displayed in the console.

You should also check that the fix introduced for KB-34325 still works, as this fix has been modified. To do that, follow the steps of #828 but with this branch.

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#taskid 41052