Polish code

code issues found by Clang with
CFLAGS="-Os -Wall -Wextra -Werror=unused-const-variable -Wno-error=unused-parameter"
enabled

The details as follows:
- variable initialization issue, modified them as Clang suggested
- data type mismatch when comparing, fix them either by casting or changing
  the data type of index of iterator
- get_sockaddr() in netutils may return -1 thus changed returning type from
  size_t to ssize_t, which makes Clang happier
- recvfrom() in udprelay is identical, fix this by creating local variable
  for comparison  and assign back to buf->len when returning value is acceptable

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

src/json.c

@@ -38,7 +38,7 @@
 #ifdef __cplusplus
 const struct _json_value json_value_none; /* zero-d by ctor */
 #else
-const struct _json_value json_value_none = { 0 };
+const struct _json_value json_value_none = { NULL, 0, {0}, {NULL} };
 #endif
 
 #include <stdio.h>
@@ -239,7 +239,7 @@ json_value *json_parse_ex(json_settings *settings,
     unsigned int cur_line;
     const json_char *cur_line_begin, *i, *end;
     json_value *top, *root, *alloc = 0;
-    json_state state = { 0 };
+    json_state state = { 0UL, 0U, 0UL, {0UL, 0, NULL, NULL, NULL}, 0 };
     long flags;
     long num_digits         = 0, num_e = 0;
     json_int_t num_fraction = 0;
@@ -933,7 +933,7 @@ e_failed:
 
 json_value *json_parse(const json_char *json, size_t length)
 {
-    json_settings settings = { 0 };
+    json_settings settings = { 0UL, 0, NULL, NULL, NULL };
     return json_parse_ex(&settings, json, length, 0);
 }
 
@@ -986,7 +986,7 @@ void json_value_free_ex(json_settings *settings, json_value *value)
 
 void json_value_free(json_value *value)
 {
-    json_settings settings = { 0 };
+    json_settings settings = { 0UL, 0, NULL, NULL, NULL };
     settings.mem_free = default_free;
     json_value_free_ex(&settings, value);
 }