Internal error while querying external dataset when other file formats are also present in same S3 bucket

Steps to reproduce :
1. Have a 2 node cluster - kv and cbas
2. Make sure AWS S3 bucket has few json files in the same path as parquet files.
2. Create external link to a AWS S3 bucket.
3. Create dataset on parquet files using external link.
4. Try to run select count(*) from dataset query.
5. Internal error is observed.
 
A better message should be displayed, letting user know that parsing failed because there were file formats apart from parquet.