Fix pointer signedness warning in sexp-conv.

ChangeLog

@@ -19,6 +19,7 @@
 	* testsuite/sexp-format-test.c (test_main): Likewise.
 	* testsuite/rsa-encrypt-test.c (test_main): Likewise.
 	* tools/nettle-lfib-stream.c (main): Likewise.
+	* tools/output.c (sexp_put_string): Likewise.
 
 	* testsuite/testutils.c (test_armor): Change ascii argument to
 	const char *.

tools/output.c

@@ -203,7 +203,7 @@ sexp_put_string(struct sexp_output *output, enum sexp_mode mode,
 {
   if (!string->size)
     sexp_put_data(output, 2,
-		  (mode == SEXP_ADVANCED) ? "\"\"": "0:");
+		  (const uint8_t *) ((mode == SEXP_ADVANCED) ? "\"\"": "0:"));
 
   else if (mode == SEXP_ADVANCED)
     {