<rdar://problem/13308704>

Fixing a problem where ValueObject::GetPointeeData() would not accept "partial" valid reads (i.e. asking for 10 items and getting only 5 back)
While suboptimal, this situation is not a flat-out failure and could well be caused by legit scenarios, such as hitting a page boundary

Among others, this allows data formatters to print char* buffers allocated under libgmalloc

llvm-svn: 193704