파이어폭스 68 버전에서 스마트에디터 오류 나는 부분을 예외처리

plugin/editor/smarteditor2/js/smarteditor2.js

@@ -20339,18 +20339,23 @@ nhn.husky.HuskyCore.mixin(nhn.husky.SE2M_TableEditor, {
 	
 	addCSSClass : function(sClassName, sClassRule){
 		var oDoc = this.oApp.getWYSIWYGDocument();
-		if(oDoc.styleSheets[0] && oDoc.styleSheets[0].addRule){
-			// IE
-			oDoc.styleSheets[0].addRule("." + sClassName, sClassRule);
-		}else{
-			// FF
-			var elHead = oDoc.getElementsByTagName("HEAD")[0]; 
-			var elStyle = oDoc.createElement ("STYLE"); 
-			//styleElement.type = "text / css"; 
-			elHead.appendChild (elStyle); 
-			
-			elStyle.sheet.insertRule("." + sClassName + " { "+sClassRule+" }", 0);
-		}
+
+        try {
+            if(oDoc.styleSheets[0] && oDoc.styleSheets[0].addRule){
+                // IE
+                oDoc.styleSheets[0].addRule("." + sClassName, sClassRule);
+            }else{
+                // FF
+                var elHead = oDoc.getElementsByTagName("HEAD")[0]; 
+                var elStyle = oDoc.createElement ("STYLE"); 
+                //styleElement.type = "text / css"; 
+                elHead.appendChild (elStyle); 
+                
+                elStyle.sheet.insertRule("." + sClassName + " { "+sClassRule+" }", 0);
+            }
+        } catch (e) {
+            //console.log(e);
+        }
 	},
 	
 	// [SMARTEDITORSUS-1533]