Value returned from a function is not checked for errors before being used

Defect 105068 (STATIC_C)
Checker CHECKED_RETURN (subcategory none)
File: /src/libmongoc/src/mongoc/mongoc-gridfs-bucket.c
Function mongoc_gridfs_bucket_open_download_stream
/src/libmongoc/src/mongoc/mongoc-gridfs-bucket.c, line: 382
Calling "bson_iter_init" without checking return value (as is done elsewhere 144 out of 177 times).

       bson_iter_init (&iter, &file_doc);