fix: prevent crash when no first responder

[kirillzyusko]

📜 Description

Prevent crash when no first responder in keyboardWillShow.

💡 Motivation and Context

It happens because we can not find first responder when keyboardWillShow is triggerred:

Then we get NPE here (read absoluteY of nil):

And finally app crashes:

To fix this problem I've decided to add guard statement - there is no sense to execute code further if we don't have a reference to TextInput - no sense to store it in holder, no sense to add listeners/observers, substitute delegates etc.

📢 Changelog

iOS

• check that first responder is actually present before executing the code that relies on its presence;

🤔 How Has This Been Tested?

Tested manually on iPhone 15.

📸 Screenshots (if appropriate):

https://github.com/kirillzyusko/react-native-keyboard-controller/assets/22820318/83ecde49-69de-483e-8403-92c4dd41c4c7

📝 Checklist

• [x] CI successfully passed
• [x] I added new mocks and corresponding unit-tests if library API was changed

[github-actions[bot]]

📊 Package size report

Current size	Target Size	Difference
136075 bytes	136074 bytes	1 bytes 📈