fix: sipflow

[yeoleobun]

For default config in the example:

[sipflow]
type = "local"
root = "./config/sipflow"
subdirs = "daily"  # "none" | "daily" | "hourly"

The subdirs option was not saved for LocalBackEnd, that does not match the query. So the query result was empty.

get_folders_in_range increment hour for dayily, that leads the sip message duplicate for the hour multiple times