bdmsupport.c: fix overflow #938

Job	Run time
build-lang	35s
build	1m 1s
build-debug (debug)	1m 17s
build-variants (RTL=0, PADEMU=0, IGS=0, DTL_T10000=0)	1m 4s
build-debug (iopcore_debug)	1m 17s
build-variants (RTL=0, PADEMU=0, IGS=0, DTL_T10000=1)	1m 8s
build-debug (ingame_debug)	1m 22s
build-variants (RTL=0, PADEMU=0, IGS=1, DTL_T10000=0)	1m 9s
build-debug (deci2_debug)	1m 7s
build-variants (RTL=0, PADEMU=0, IGS=1, DTL_T10000=1)	1m 9s
build-debug (eesio_debug)	1m 14s
build-variants (RTL=0, PADEMU=1, IGS=0, DTL_T10000=0)	1m 6s
build-variants (RTL=0, PADEMU=1, IGS=0, DTL_T10000=1)	1m 6s
build-variants (RTL=0, PADEMU=1, IGS=1, DTL_T10000=0)	1m 7s
build-variants (RTL=0, PADEMU=1, IGS=1, DTL_T10000=1)	1m 6s
build-variants (RTL=1, PADEMU=0, IGS=0, DTL_T10000=0)	1m 7s
build-variants (RTL=1, PADEMU=0, IGS=0, DTL_T10000=1)	1m 3s
build-variants (RTL=1, PADEMU=0, IGS=1, DTL_T10000=0)	1m 11s
build-variants (RTL=1, PADEMU=0, IGS=1, DTL_T10000=1)	1m 15s
build-variants (RTL=1, PADEMU=1, IGS=0, DTL_T10000=0)	1m 11s
build-variants (RTL=1, PADEMU=1, IGS=0, DTL_T10000=1)	1m 10s
build-variants (RTL=1, PADEMU=1, IGS=1, DTL_T10000=0)	1m 12s
build-variants (RTL=1, PADEMU=1, IGS=1, DTL_T10000=1)	1m 13s
merge-debug	5s
merge-variants	13s
release	0s
	26m 28s

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