Ignore static rules with not exactly one argument

[jreinhardt]

I came across this when I tried to freeze one of my flask apps with frozen-flask, where I did use url_defaults and url_value_preprocessor. It took me a while to figure out, why Frozen-flask did react like it did.

This just skips those rules, the logic from the value_preprocessor needs to be captured in a custom generator.

[honzajavorek]

@jreinhardt Hi, I'm sorry it took us a while to get to this. Would you be willing to share a test case as well, or a comment reproducing the situations you're trying to solve here?

[liZe]

Don’t hesitate to add a comment if you think that this PR could be useful.