Handle not implemented renderer-type

[Kanahiro]

https://github.com/MIERUNE/qgis-plugin-for-plugx/blob/8238ce9302c7b6a5a051562cc090ee760641583b/translator/vector/process.py#L107

this method has a problem:

• if renderer-type is not "categorized" or "graduated" or "single", result will be undefined and error will occur.