Handle template creation failures with the template engine

Check the status of the result and throw an exception with
information about the failure. This will aid diagnosing problems
with the template. Previously a null reference exception would
be thrown as an attempt was made to use the TemplateCreationResult's
ResultInfo which would be null.

Author: mrward

src/MonoDevelop.TemplateCreator/MonoDevelop.Templating/TemplateProcessor.cs

@@ -74,6 +74,11 @@ public async Task<ProcessedTemplateResult> ProcessTemplate ()
 			var parameters = new Dictionary<string, string> ();
 			var result = await templateEngine.Create (template, config, parameters);
 
+			if (result.Status != CreationResultStatus.Success) {
+				string message = GettextCatalog.GetString ("Could not create template. Id='{0}' {1} {2}", template.Id, result.Status, result.Message);
+				throw new InvalidOperationException (message);
+			}
+
 			List<string> filesToOpen = GetFilesToOpen (result).ToList ();
 			workspaceItems = await GetWorkspaceItems (result);