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

Defect 49573 (STATIC_C)
Checker CHECKED_RETURN (subcategory none)
File: /src/mongoc/mongoc-collection.c
Function mongoc_collection_save
/src/mongoc/mongoc-collection.c, line: 1330
Calling "bson_append_iter" without checking return value (as is done elsewhere 3 out of 4 times).

       bson_append_iter(&selector, NULL, 0, &iter);