gpgkey2ssh: clean up varargs

* tools/gpgkey2ssh.c (key_to_blob) : ensure that va_end is called.

--

stdarg(3) says:
       Each invocation of va_start() must be matched by a
       corresponding invocation of va_end() in the same function.

Observed by Joshua Rogers <honey@internot.info>

Debian-Bug-Id: 773415

tools/gpgkey2ssh.c

@@ -224,6 +224,8 @@ key_to_blob (unsigned char **blob, size_t *blob_n, const char *identifier, ...)
       assert (ret == 1);
     }
 
+  va_end (ap);
+
   blob_new_n = ftell (stream);
   rewind (stream);