xdrgen: Initialize data pointer for zero-length items

xdrgen: Initialize data pointer for zero-length items

The xdrgen decoders for strings and opaque data had an
optimization that skipped calling xdr_inline_decode() when the
item length was zero. This left the data pointer uninitialized,
which could lead to unpredictable behavior when callers access
it.

Remove the zero-length check and always call xdr_inline_decode().
When passed a length of zero, xdr_inline_decode() returns the
current buffer position, which is valid and matches the behavior
of hand-coded XDR decoders throughout the kernel.

Fixes: 4b132aacb076 ("tools: Add xdrgen")
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: NeilBrown <neil@brown.name>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>