fix: Platform add hangs when invalid frameworkPath is passed

[rosen-vladimirov]

In case non-existent file is passed to --frameworkPath the tns platform add ... command hangs. Fix this by checking if the passed value is correct.

PR Checklist

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What is the current behavior?

tns platform add android --frameworkPath invalid.tgz hangs.

What is the new behavior?

tns platform add android --frameworkPath invalid.tgz fails with error: Invalid frameworkPath: invalid.tgz. Please ensure the specified frameworkPath exists.