api: Remove arbitrary restriction from gpgme_op_verify.

* src/verify.c (verify_start): Do not return GPG_ERR_INV_VALUES when
when SIGNED_TEXT is not given.
--

The original idea behind this restriction probably was that it is
useless to verify a non-detached signatures without also returning the
signed text.  However, it is sometimes useful to just check the
signature, for example to see who signed it.

Signed-off-by: Werner Koch <wk@gnupg.org>

src/verify.c

@@ -861,8 +861,6 @@ verify_start (gpgme_ctx_t ctx, int synchronous, gpgme_data_t sig,
 
   if (!sig)
     return gpg_error (GPG_ERR_NO_DATA);
-  if (!signed_text && !plaintext)
-    return gpg_error (GPG_ERR_INV_VALUE);
 
   return _gpgme_engine_op_verify (ctx->engine, sig, signed_text, plaintext);
 }