fix: Publish toolbar dissappears when submitting empty content

What does this MR do?

To detect that the content was loaded successfully, the Static Site Editor verifies that the originalContent property is not empty. When the user removes all the content of a page a submits the changes successfully, the originalContent property becomes empty and the Static Site Editor thinks that the content is not loaded again.

This MR decouples identifying if the content is loaded from originalContent to prevent this bug.

Before	After

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content