Fix crash with "wrap-lines" text editor operation if prefix or suffix…

… is missing

Fixes #6376

core/modules/editor/operations/text/wrap-lines.js

@@ -13,15 +13,17 @@ Text editor operation to wrap the selected lines with a prefix and suffix
 "use strict";
 
 exports["wrap-lines"] = function(event,operation) {
+	var prefix = operation.paramObject.prefix || "",
+		suffix = operation.paramObject.suffix || "";
 	// Cut just past the preceding line break, or the start of the text
 	operation.cutStart = $tw.utils.findPrecedingLineBreak(operation.text,operation.selStart);
 	// Cut to just past the following line break, or to the end of the text
 	operation.cutEnd = $tw.utils.findFollowingLineBreak(operation.text,operation.selEnd);
 	// Add the prefix and suffix
-	operation.replacement = event.paramObject.prefix + "\n" +
+	operation.replacement = prefix + "\n" +
 				operation.text.substring(operation.cutStart,operation.cutEnd) + "\n" +
-				event.paramObject.suffix + "\n";
-	operation.newSelStart = operation.cutStart + event.paramObject.prefix.length + 1;
+				suffix + "\n";
+	operation.newSelStart = operation.cutStart + prefix.length + 1;
 	operation.newSelEnd = operation.newSelStart + (operation.cutEnd - operation.cutStart);
 };