Fix nil data case

Author: root

Diff for: lib/redmine_git_hosting/redmine_plugin_loader.rb

@@ -114,7 +114,8 @@ def load_plugin!
 
       def load_setting_file(file)
         return {} unless File.exists?(file)
-        YAML::load(ERB.new(IO.read(file)).result).symbolize_keys
+        data = YAML::load(ERB.new(IO.read(file)).result) || {}
+        data.symbolize_keys
       end