phonenumber: panic on parsing crafted RF3966 phonenumber inputs

Impact

The phonenumber parsing code may panic due to a panic-guarded out-of-bounds access on the phonenumber string.

In a typical deployment of rust-phonenumber, this may get triggered by feeding a maliciously crafted phonenumber over the network, specifically the string .;phone-context=.

Patches

Patches will be published as version 0.3.3+8.13.9 and backported as 0.2.5+8.11.3.