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.