sys/threads: add assert(mutex_get(h) >= 0) #1130

Job	Run time
call-ci / build (armv7a7-imx6ull-evk)	1m 23s
call-ci / build (armv7a9-zynq7000-qemu)	1m 17s
call-ci / build (armv7a9-zynq7000-zedboard)	1m 9s
call-ci / build (armv7a9-zynq7000-zturn)	1m 7s
call-ci / build (armv7m4-stm32l4x6-nucleo)	1m 22s
call-ci / build (armv7m7-imxrt105x-evk)	1m 24s
call-ci / build (armv7m7-imxrt106x-evk)	1m 21s
call-ci / build (armv7m7-imxrt117x-evk)	1m 32s
call-ci / build (host-generic-pc)	1m 10s
call-ci / build (ia32-generic-pc)	1m 6s
call-ci / build (ia32-generic-qemu)	1m 4s
call-ci / build (riscv64-generic-qemu)	58s
call-ci / build (riscv64-generic-spike)	1m 37s
call-ci / build (sparcv8leon3-gr716-mini)	59s
call-ci / test EMU (armv7a9-zynq7000-qemu)	49m 32s
call-ci / test HW (armv7a7-imx6ull-evk)	28m 49s
call-ci / test EMU (host-generic-pc)	1m 3s
call-ci / test HW (armv7m7-imxrt106x-evk)	3m 52s
call-ci / test EMU (ia32-generic-qemu)	25m 3s
call-ci / test HW (armv7m7-imxrt117x-evk)	4m 5s
call-ci / test EMU (riscv64-generic-qemu)	24m 16s
call-ci / test HW (armv7a9-zynq7000-zedboard)	29m 21s
call-ci / test HW (armv7m4-stm32l4x6-nucleo)	11m 40s
call-ci / tests-summary	8s
call-ci / send-notification	0s
	3h 15m 18s

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