bpo-30414: multiprocessing.Queue._feed do not break from main loop on exc (#1683)

* bpo-30414: multiprocesing.Queue._feed do not break from main loop on exc

Queue background running thread was not handling exceptions correctly.
Any exception occurred inside thread (putting unpickable object) cause
feeder to finish running. After that every message put into queue is
silently ignored.

* bpo-30414: multiprocesing.Queue._feed do not break from main loop on exc

Queue background running thread was not handling exceptions correctly.
Any exception occurred inside thread (putting unpickable object) cause
feeder to finish running. After that every message put into queue is
silently ignored.