Steps to reproduce the issue

in global configuration change site offline to yes

Expected result

preview of image which as its not set yet is the blank default

Actual result

it tries to load a non-existent file.

		<div class="field-media-preview">
			 <div id="jform_offline_image_preview_empty">No image selected.</div>
			 	 <div id="jform_offline_image_preview_img">
			 	 	 <img src="" alt="Selected image." id="jform_offline_image_preview" class="media-preview" style="max-width:200px;max-height:200px;">
			 	 </div>	
		</div>

Additional comments

I suspect this is a javascript issue a