backwards is OK.) Otherwise, do nothing.
ASSERT_VALID_BYTIND_FORWARD_UNSAFE(buf, bi):
If error-checking is enabled, assert that the given byte index
is within range and satisfies ASSERT_VALID_BYTIND() and also
backwards is OK.) Otherwise, do nothing.
ASSERT_VALID_BYTIND_FORWARD_UNSAFE(buf, bi):
If error-checking is enabled, assert that the given byte index
is within range and satisfies ASSERT_VALID_BYTIND() and also