ZJIT: x86: Fix panic writing 32-bit number with top bit set #620

Job	Run time
omnibus compilations, trigger	2s
omnibus compilations, #2	32m 47s
omnibus compilations, #1	27m 42s
omnibus compilations, #5	26m 25s
omnibus compilations, #6	26m 56s
omnibus compilations, #8	27m 0s
omnibus compilations, #10	26m 25s
omnibus compilations, #11	27m 13s
omnibus compilations, #12	24m 20s
omnibus compilations, #3	29m 52s
omnibus compilations, #7	32m 39s
omnibus compilations, #9	27m 33s
omnibus compilations, #4	25m 19s
omnibus compilations, result	4s
	5h 34m 17s

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