[llvm-objcopy] [COFF] Don't call memcpy() with a null argument. NFC.
[llvm-objcopy] [COFF] Don't call memcpy() with a null argument. NFC.

It is invalid to call memcpy with a null pointer, even if the size
is zero.

This should fix the sanitizer buildbot.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@349808 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm