minor bugfix to expanding images with loading bars enabled

even though the image is a blob, when we set the src={blob}, it doesnt load immediately
thus, the offsetWidth is 0 and when expanding, the filename width is wrong (only on the first time expanding, since subsequent times, the blob has "loaded" already and now has an offsetWidth -- it is almost instant).
this adds and onload to wait for the image to "load", and thus has the correct width even on the first time when expanding

gulp/res/js/expand.js

@@ -122,11 +122,13 @@ window.addEventListener('DOMContentLoaded', (event) => {
 								pfs.removeAttribute('data-loading');
 								pfs.removeAttribute('style');
 								const blob = this.response;
+								source.onload = function() {
+									thumbElement.style.opacity = '';
+									thumbElement.style.cursor = '';
+									fileAnchor.appendChild(expandedElement);
+									toggle(thumbElement, expandedElement, fileName, pfs);
+								}
 								source.src = window.URL.createObjectURL(blob);
-								thumbElement.style.opacity = '';
-								thumbElement.style.cursor = '';
-								fileAnchor.appendChild(expandedElement);
-								toggle(thumbElement, expandedElement, fileName, pfs);
 							}
 							request.onload = loaded;
 							request.responseType = 'blob';