fix: prevent crashes on setDataSource failure and missing native module

[gandol]

Summary

• Android: Catch Exception (including RuntimeException from MediaMetadataRetriever.setDataSource) so bad/unsupported video URLs reject the JS Promise instead of crashing the Android process
• Android: Validate empty video URLs early; always release the retriever in finally; coerce headers to Map<String, String>
• JS: Guard exports when the native module is not linked so import-time destructuring does not crash

Problem

1. Android process crash (setDataSource)

On Android, MediaMetadataRetriever.setDataSource can throw:

java.lang.RuntimeException: setDataSource failed: status = 0x80000000

This happens for empty URLs, unsupported codecs, or remote videos the retriever cannot open. The previous catch block only handled IOException | IllegalStateException, so the uncaught RuntimeException on the worker thread killed the entire app:

FATAL EXCEPTION: pool-*-thread-1
java.lang.RuntimeException: setDataSource failed: status = 0x80000000
  at android.media.MediaMetadataRetriever.setDataSource
  at CreateThumbnailModule.getBitmapAtTime

JS .catch() never runs because the process dies before the Promise is rejected.

Related: #62, #131

2. JS crash when native module is missing

export const { create: createThumbnail } = CreateThumbnail;

throws if CreateThumbnail is undefined (Expo Go, incomplete autolinking, etc.). This change uses optional chaining and rejects the Promise instead.

Test plan

• Call createThumbnail with a valid local/remote video URL → still resolves with a thumbnail
• Call with an empty url → Promise rejects with CreateThumbnail_ERROR (no crash)
• Call with a bad/unsupported remote URL (e.g. one that previously caused 0x80000000) → Promise rejects (no crash)
• Call with optional headers → still works
• Load the package when native module is not linked → import succeeds; createThumbnail() rejects (no crash)