replace src if background image cannot be inserted

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

@@ -1079,10 +1079,8 @@ this.SingleFileCore = this.SingleFileCore || (() => {
 								resourceElement.remove();
 							} else {
 								if (content.startsWith(prefixDataURI) || content.startsWith(PREFIX_DATA_URI_NO_MIMETYPE) || content.startsWith(PREFIX_DATA_URI_OCTET_STREAM)) {
-									if (processDuplicates && duplicate && options.groupDuplicateImages) {
-										if (DomUtil.replaceImageSource(resourceElement, SINGLE_FILE_VARIABLE_NAME_PREFIX + indexResource, options)) {
-											DomUtil.insertVariable(doc, indexResource, content, options);
-										}
+									if (processDuplicates && duplicate && options.groupDuplicateImages && DomUtil.replaceImageSource(resourceElement, SINGLE_FILE_VARIABLE_NAME_PREFIX + indexResource, options)) {
+										DomUtil.insertVariable(doc, indexResource, content, options);
 									} else {
 										resourceElement.setAttribute(attributeName, content);
 									}