Do not normalize an implausible phone

It can generate an unexpected string. Example:

````ruby
Phony.normalize("01")
=> "1[#<Phony::NationalCode:0x007fc0745223a8 @national_splitter=#<Phony::NationalSplitters::Fixed:0x007fc074522448 @size=3, @zero=nil>, @local_splitter=#<Phony::LocalSplitters::Fixed:0x007fc07442d790 @format=[3, 14]>, @normalize=true>]"
````