SOLIDPOD: Fix `readExternalPod()` for extracting non-ttl files

[anushkavidanage]

Currently readExternalPod() throws an error when reading non encrypted non-ttl file content in an external POD. This is because the function tries to read the file content as a ttl by parsing the string.

[gjwgit]

Thanks for noting this issue. Yes readExternalPod() should handle any file type.

[gjwgit]

This is likely okay now we have merged readExternalPod into readPod - @anushka to do a quick check then can close.

[gjwgit]

@cdawei to do a quick confirmation then we can close this issue.

[cdawei]

Confirm that readExternalPod() can successfully read a unencrypted .txt file in an external POD. Checked with solidui example app.

[gjwgit]

Thanks @cdawei Closing this now.