crypto: user - fix empty string test in report API

The current test for empty strings fails because it is testing the
address of a field, not a pointer. So the test will always be true.
Test the first character in the string to not be null instead.

Signed-off-by: Mathias Krause <minipli@googlemail.com>
Cc: Steffen Klassert <steffen.klassert@secunet.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>