reintoduced basic support of lazy loading

lib/single-file/single-file-core.js

@@ -441,6 +441,24 @@ this.SingleFileCore = this.SingleFileCore || (() => {
 						imgElement.setAttribute("src", imgData.src);
 					}
 				});
+				if (this.options.lazyLoadImages) {
+					this.doc.querySelectorAll("img[data-srcset]").forEach(imgElement => {
+						const imgData = this.options.imageData[Number(imgElement.getAttribute(dataAttributeName))];
+						if (!imgData.srcset && imgElement.getAttribute("data-srcset")) {
+							imgElement.setAttribute("srcset", imgElement.dataset.srcset);
+							imgElement.removeAttribute("data-srcset");
+						}
+					});
+					this.doc.querySelectorAll("img[data-src]").forEach(imgElement => {
+						const imgData = this.options.imageData[Number(imgElement.getAttribute(dataAttributeName))];
+						if ((!imgData.src || imgData.empty) && !imgData.srcset && imgElement.getAttribute("data-src")) {
+							imgData.src = imgElement.dataset.src;
+							imgData.empty = false;
+							imgElement.setAttribute("src", imgElement.dataset.src);
+							imgElement.removeAttribute("data-src");
+						}
+					});
+				}
 			}
 		}