[3.9][JLayout images] Remove unnecessary isset(...)

[ReLater]

Testing Instructions

• Code review. We don't need the additional isset(...) check because !empty(...) is sufficient.

Expected result

• No changes with output of intro images in category blogs and featured blogs
• No changes with output of full images in article views

Actual result

• Unnecessary code.

[Quy]

I have tested this item ✅ successfully on 7d9faeb

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/24390.}

[SharkyKZ]

I have tested this item ✅ successfully on 7d9faeb

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/24390.}

[ghost]

Status "Ready To Commit".

[HLeithner]

thx