Fix the bug when sender was never dropped #1086

Job	Run time
Basic Checks	7m 49s
Additional Builds and Concurrency Tests	15m 16s
Slow tests	16m 11s
Release builds and tests	8m 15s
Measure coverage	28m 10s
miri	3m 3s
sanitize (address)	19m 7s
sanitize (address, multi-threading)	19m 45s
sanitize (leak)	3m 55s
sanitize (leak, multi-threading)	3m 48s
	2h 5m 19s

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