message: fix HeapFree return value
diff: @@ -722,6 +722,7 @@ pub trait EvalContextExt<'a, 'mir, 'tcx: 'a + 'mir>: crate::MiriEvalContextExt<'
  // Windows API stubs.
  // HANDLE = isize
  // DWORD = ULONG = u32
  + // BOOL = i32
  "GetProcessHeap" => {
  // Just fake a HANDLE
  this.write_scalar(Scalar::from_int(1, this.pointer_size()), dest)?;
  @@ -739,6 +740,7 @@ pub trait EvalContextExt<'a, 'mir, 'tcx: 'a + 'mir>: crate::MiriEvalContextExt<'
  let _flags = this.read_scalar(args[1])?.to_u32()?;
  let ptr = this.read_scalar(args[2])?.not_undef()?;
  this.free(ptr)?;
  + this.write_scalar(Scalar::from_int(1, Size::from_bytes(4)), dest)?;
  }
  "HeapReAlloc" => {
  let _handle = this.read_scalar(args[0])?.to_isize(this)?;
  