reader: add missing case for reaching eof.
reader: add missing case for reaching eof.

mongodbinc-interns/libbson,rayyang2000/libbson,hanumantmk/libbson,remicollet/libbson,ksuarz/libbson,Convey-Compliance/libbson,mapr/libbson,bjori/libbson,derickr/libbson,Convey-Compliance/libbson,rcsanchez97/libbson,remicollet/libbson,rcsanchez97/libbson,bjori/libbson,ajdavis/libbson,rcsanchez97/libbson,hanumantmk/libbson,Convey-Compliance/libbson,ksuarz/libbson,alexeyvo/libbson,mongodb/libbson,mongodbinc-interns/libbson,4Second2None/libbson_tmp,rayyang2000/libbson,bjori/libbson,mapr/libbson,ajdavis/libbson,hanumantmk/libbson,Machyne/libbson,alexeyvo/libbson,derickr/libbson,paulmelnikow/libbson,paulmelnikow/libbson,jqk6/libbson,paulmelnikow/libbson,jqk6/libbson,jqk6/libbson,ksuarz/libbson,4Second2None/libbson_tmp,derickr/libbson,4Second2None/libbson_tmp,paulmelnikow/libbson,mongodbinc-interns/libbson,Machyne/libbson,4Second2None/libbson_tmp,jqk6/libbson,mongodbinc-interns/libbson,Machyne/libbson,ajdavis/libbson,paulmelnikow/libbson,mongodb/libbson,derickr/libbson,rayyang2000/libbson,rayyang2000/libbson,mongodb/libbson,alexeyvo/libbson,hanumantmk/libbson,mapr/libbson,remicollet/libbson,Machyne/libbson,remicollet/libbson