g10: Fix memory leak for PKT_signature.

* g10/getkey.c (buf_to_sig): Free by free_seckey_enc.
* g10/gpgcompose.c (signature): Likewise.
* g10/sign.c (write_signature_packets): Likewise.

--

Cherry picked from master commit:
    996febbab2

Reported-by: Philippe Antoine
GnuPG-bug-id: 4047
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>

g10/getkey.c

@@ -3128,7 +3128,7 @@ buf_to_sig (const byte * buf, size_t len)
 
   if (parse_signature (iobuf, PKT_SIGNATURE, len, sig) != 0)
     {
-      xfree (sig);
+      free_seckey_enc (sig);
       sig = NULL;
     }
 

g10/gpgcompose.c

@@ -1835,7 +1835,7 @@ signature (const char *option, int argc, char *argv[], void *cookie)
   debug ("Wrote signature packet:\n");
   dump_component (&pkt);
 
-  xfree (sig);
+  free_seckey_enc (sig);
   release_kbnode (si.issuer_kb);
   xfree (si.revocation_key);
 

g10/sign.c

@@ -772,7 +772,7 @@ write_signature_packets (ctrl_t ctrl,
                        gpg_strerror (rc));
 	}
       else
-        xfree (sig);
+        free_seckey_enc (sig);
 
       if (rc)
         return rc;