Fix casting to signed unnormalized integers.
Fix casting to signed unnormalized integers.

Change-Id: Ic1e4256bd73281af3e48d0f81ad16ea92a60ce4f
Reviewed-on: https://swiftshader-review.googlesource.com/14368
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Tested-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>

bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader