added response check for swagger 2.0/1.2 client

lib/swagger-client.js

@@ -184,6 +184,7 @@ var SwaggerClient = function(url, options) {
   this.basePath = null;
   this.authorizations = null;
   this.authorizationScheme = null;
+  this.isValid = false;
   this.info = null;
   this.useJQuery = false;
 
@@ -236,6 +237,11 @@ SwaggerClient.prototype.build = function() {
         if(responseObj.swagger && responseObj.swagger === 2.0) {
           self.swaggerVersion = responseObj.swagger;
           self.buildFromSpec(responseObj);
+          self.isValid = true;
+        }
+        else {
+          self.isValid = false;
+          self.failure()
         }
       }
     }