fuzz:afl main: add a diagnostic message

LLVMFuzzerTestOneInput() NEVER returns non-zero, but if it does, we might as well
know what made it do so

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Jeremy Allison <jra@samba.org>

lib/fuzzing/afl-fuzz-main.c

@@ -38,6 +38,8 @@ int main(int argc, char *argv[]) {
 		ret = LLVMFuzzerTestOneInput(buf, size);
 		TALLOC_FREE(buf);
 		if (ret != 0) {
+			printf("LLVMFuzzerTestOneInput returned %d on argument %d\n",
+			       ret, i);
 			return ret;
 		}
 	}