json_load_file: Initialize the error struct properly

Failing to do this has the effect that the error message is not
returned when the input file cannot be opened (e.g. if it doesn't
exist).

Thanks to Martin Vopatek for reporting.

src/load.c

@@ -864,6 +864,8 @@ json_t *json_load_file(const char *path, json_error_t *error)
     json_t *result;
     FILE *fp;
 
+    error_init(error);
+
     fp = fopen(path, "r");
     if(!fp)
     {

test/.gitignore

@@ -3,6 +3,7 @@ loads_dumps
 load_file_dump_file
 testlogs
 testprogs/test_array
+testprogs/test_load
 testprogs/test_number
 testprogs/test_object
 testprogs/test_simple

test/testprogs/Makefile.am

@@ -1,6 +1,7 @@
-check_PROGRAMS = test_array test_simple test_number test_object
+check_PROGRAMS = test_array test_load test_simple test_number test_object
 
 test_array_SOURCES = test_array.c util.h
+test_load_SOURCES = test_load.c util.h
 test_simple_SOURCES = test_simple.c util.h
 test_number_SOURCES = test_number.c util.h
 test_object_SOURCES = test_object.c util.h

test/testprogs/test_load.c

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2009 Petri Lehtinen <petri@digip.org>
+ *
+ * Jansson is free software; you can redistribute it and/or modify
+ * it under the terms of the MIT license. See LICENSE for details.
+ */
+
+#include <jansson.h>
+#include <string.h>
+#include "util.h"
+
+int main()
+{
+    json_t *json;
+    json_error_t error;
+
+    json = json_load_file("/path/to/nonexistent/file.json", &error);
+    if(error.line != -1)
+        fail("json_load_file returned an invalid line number");
+    if(strcmp(error.text, "unable to open /path/to/nonexistent/file.json: No such file or directory") != 0)
+        fail("json_load_file returned an invalid error message");
+
+    return 0;
+}