csvsql fails with misleading error if query and dialect are specified with no connection_string

Created by: chisco50

Behavior If I try to run csvsql with "dialect", "query" and no "connection_string", it will fail with a "The --dialect option is only valid when --db is not specified."

Cause: Given that both "query" and "dialect" are being used, the run enters the following block which sets a default connection_string

# Create an SQLite database in memory if no connection string is specified```
        if query and not connection_string:
            connection_string = "sqlite:///:memory:"
            do_insert = True```

Then, the following block will always raise the error as there is now a connection string and a dialect:

if self.args.dialect and connection_string:
            self.argparser.error('The --dialect option is only valid when --db is not specified.')

Suggestion: Refactor the code (csvsql.py). One quick possibility is to call the block that raises the error before the block that sets the default connection string.