Check for null when using UriResolverExtensionFileReader to read wasm module

[krisbitney]

When a Wasm wrapper dev tries to invoke an interface in their wrapper, an error isn't thrown in the wasm-js package. Instead of returning a UInt8Array containing a Wasm pacakge, the _getWasmModule method in WasmWrapper.ts returns null. The null value is passed around until a null pointer exception is thrown when trying to call indexOf on it in the indexOfArray method in utils.ts in the asyncify-js package.

The null value arrises because the UriResolverExtensionFileReader in the uri-resolver-extensions package wants to return a UInt8Array or an error. However, thegetFile method of the uri resolver interface returns Bytes | null. All of the uri resolver implementations return null on failure. So we need to check that the retrieved file data is not null.

[dOrgJelli]

Great find!