catch json-parse error

src/js/simplemde.js

@@ -679,10 +679,14 @@ function uploadImage(editor) {
 		xmlhttp.send(formData);
 		xmlhttp.onreadystatechange = function() {
 			if(xmlhttp.readyState == 4 && xmlhttp.status == 200) {
+				try {
 					var res = JSON.parse(xmlhttp.responseText);
 					if(res.url) {
 						editor.codemirror.replaceSelection("![" + (res.name || file.name) + "](" + res.url + ")");
 					}
+				} catch (e) {
+					editor.codemirror.replaceSelection("![]()");
+				}
 			}
 		};