Subzero: fix Ice::BitVector::grow not copying old to new data
Subzero: fix Ice::BitVector::grow not copying old to new data

UBSAN pointed out that memcpy cannot have nullptr dest or source,
which I've also fixed; however, this also made me realize a latent bug:
the dest and source args needed to be swapped. It seems this bug hasn't
bit us yet because the normal use-case is to resize the bitvector, and
then call 'set' to set all bits to 0 or 1. In any case, still worth
fixing.

Bug: b/171581990
Change-Id: Iaaa7e019b53ae661f49c97195f2d144b5715f164
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/49528
Presubmit-Ready: Antonio Maiorano <86d87a6550afb6b07035c9743fa181900589f7e0@google.com>
Reviewed-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Kokoro-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Tested-by: Antonio Maiorano <86d87a6550afb6b07035c9743fa181900589f7e0@google.com>

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