Crash when initially wrong number provided

[Michał Karnicki]

Reproduce with:

in uitest/ui/SignInPage.qml comment out the following, so you can pass the phone number twice:
// userTextField.enabled = false;
// signInButton.enabled = false;

1) rm -rf ./libqtelegram
2) launch uitest app
3) pass as phone number: +0000000000
4) note the error string
5) pass a correct phone number
6) observe the crash