fix: works correctly with projects with .nsconfig file on tns preview command

[Fatme]

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
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• Tests for the changes are included.

What is the current behavior?

An error is thrown on projects with .nsconfig file when tns preview command is executed

What is the new behavior?

Works correctly on projects with .nsconfig file when tns preview command is executed

Steps to reproduce:

1. tns create myApp --template https://github.com/NativeScript/template-hello-world-ng/tarball/master
2. cd myApp
3. tns preview
4. Apply a change in the code

[Fatme]

run ci

[rosen-vladimirov]

run ci