Display error if TFTP field empty

If either TFTP Server IP Address or File Name is empty for the
"Download image file from TFTP server" function, return and
display an error.

Tested: Verified I see this error if either field is empty.

Change-Id: I3da3353dad7cfb0f765d8a662412c3adb3fa4efd
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/app/configuration/controllers/firmware-controller.js b/app/configuration/controllers/firmware-controller.js
index 127a7c2..29d0412 100644
--- a/app/configuration/controllers/firmware-controller.js
+++ b/app/configuration/controllers/firmware-controller.js
@@ -49,6 +49,7 @@
                     $scope.file_empty = true;
                     $scope.uploading = false;
                     $scope.activate = { reboot: true };
+                    $scope.download_error_msg = "";
 
                     var pollActivationTimer = undefined;
 
@@ -156,6 +157,11 @@
                     }
 
                     $scope.download = function(){
+                        $scope.download_error_msg = "";
+                        if(!$scope.download_host || !$scope.download_filename){
+                            $scope.download_error_msg = "Field is required!";
+                            return false;
+                        }
                         $scope.downloading = true;
                         APIUtils.downloadImage($scope.download_host, $scope.download_filename).then(function(response){
                             var data = response.data;