fix parsing json response with charset

plugins/c9.core/http-xhr.js

@@ -66,7 +66,7 @@ define(function(require, module, exports) {
                         return done(new Error("Could not serialize body as json"));
                     }
                 }
-                if (contentType.indexOf("application/x-www-form-urlencoded") === 0) {
+                else if (contentType.indexOf("application/x-www-form-urlencoded") === 0) {
                     body = qs.stringify(body);
                 }
                 else if (["[object File]", "[object Blob]"].indexOf(Object.prototype.toString.call(body)) > -1) {
@@ -75,7 +75,7 @@ define(function(require, module, exports) {
                 }
                 else {
                     body = body.toString();
-                }    
+                }
             }
             
             var timer;
@@ -105,18 +105,15 @@ define(function(require, module, exports) {
                     headers: parseHeaders(xhr.getAllResponseHeaders())
                 };
                 
-                var data;
-                switch (options.overrideMimeType || res.headers["content-type"]) {
-                    case "application/json":
-                        try {
-                            data = JSON.parse(xhr.responseText);
-                        } catch (e) {
-                            return done(e); 
-                        }
-                        break;
-                    default:
-                        data = xhr.responseText;
-                        
+                var data = xhr.responseText;
+                if ((options.overrideMimeType || res.headers["content-type"])
+                    .indexOf("application/json") === 0
+                ) {
+                    try {
+                        data = JSON.parse(data);
+                    } catch (e) {
+                        return done(e);
+                    }
                 }
                 
                 if (this.status > 299) {