Fuzz test failure in lossless_cast

[steven-johnson]

From https://buildbot.halide-lang.org/master/#/builders/163/builds/31:

lossless_cast failure
seed = 1983253908
x = 0
buf_u8 = 25
buf_i8 = 64
out1 = -29
out2 = 131
Original: (int64(int32(uint16((uint8)buf_u8(x))))*int64(((((uint8)106 - (uint8)127) + (uint8)11)*uint8((uint16)rounding_shift_right(uint16((uint8)buf_u8(x)), (uint16)11)))))
Lossless cast: (uint16((uint8)buf_u8(x))*uint16(((((uint8)106 - (uint8)127) + (uint8)11)*uint8((uint16)rounding_shift_right(uint16((uint8)buf_u8(x)), (uint16)11)))))
lossless_cast fuzz test failed!

[steven-johnson]

Does not repro for me on osx 64-bit -- maybe only on 32-bit targets? Will try to repro

[steven-johnson]

Unable to repeat locally with a 32-bit linux build.