ignore invalid regular expressions (fix #721)

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

@@ -1664,7 +1664,11 @@ class ProcessorHelper {
 						}
 					}
 					if (testValidURL(resolvedURL) && resourceURL != resolvedURL && stylesheetContent.includes(urlFunction)) {
-						stylesheetContent = stylesheetContent.replace(getRegExp(urlFunction), originalResourceURL ? urlFunction.replace(originalResourceURL, resolvedURL) : "url(" + resolvedURL + ")");
+						try {
+							stylesheetContent = stylesheetContent.replace(getRegExp(urlFunction), originalResourceURL ? urlFunction.replace(originalResourceURL, resolvedURL) : "url(" + resolvedURL + ")");
+						} catch (error) {
+							// ignored
+						}
 					}
 				} else {
 					let newUrlFunction;