Guard against overflow in blur code #2015

Job	Run time
raspi-2 / initialize	47s
raspi-2-skia / initialize	42s
raspi-2-skia / docker-build-image	2m 29s
raspi-2-skia / docker-unittest-image	0s
raspi-2 / docker-build-image	2m 37s
raspi-2 / docker-unittest-image	0s
raspi-2-skia / raspi-2-skia_devel	10m 40s
raspi-2-skia / raspi-2-skia_debug	14m 21s
raspi-2-skia / raspi-2-skia_qa	9m 9s
raspi-2-skia / raspi-2-skia_gold	9m 37s
raspi-2 / raspi_devel	11m 6s
raspi-2 / raspi_debug	14m 26s
raspi-2 / raspi_qa	9m 34s
raspi-2 / raspi_gold	9m 13s
raspi-2 / sbversion-15_devel	10m 41s
raspi-2 / sbversion-15_debug	14m 30s
raspi-2 / sbversion-15_qa	9m 10s
raspi-2 / sbversion-15_gold	9m 7s
raspi-2 / sbversion-16_devel	10m 33s
raspi-2 / sbversion-16_debug	14m 43s
raspi-2 / sbversion-16_qa	9m 59s
raspi-2 / sbversion-16_gold	9m 13s
raspi-2-skia / ${{ matrix.name }}_on_device_${{ matrix.shard }}	0s
raspi-2-skia / ${{ matrix.name }}_${{ matrix.shard }}_test	0s
raspi-2 / ${{ matrix.name }}_${{ matrix.shard }}_test	0s
raspi-2 / ${{ matrix.name }}_on_device_${{ matrix.shard }}	0s
	3h 2m 37s

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