Merge pull request #315 from github/fixes/create-branch-NRE

Fix NullReferenceException during branch create

Author: shana

src/UnityExtension/Assets/Editor/GitHub.Unity/UI/BranchesView.cs

@@ -464,6 +464,7 @@ private void OnCreateGUI()
                     var cancelCreate = false;
                     var cannotCreate = selectedNode == null ||
                                        selectedNode.Type == NodeType.Folder ||
+                                       newBranchName == null ||
                                        !Utility.BranchNameRegex.IsMatch(newBranchName);
 
                     // Create on return/enter or cancel on escape