Lots of cppcheck warnings

[Harvie]

$ cppcheck --force .
Checking frozen.c ...
frozen.c:866:49: error: Pointer addition with NULL pointer. [nullPointerArithmetic]
  char *send = (char *) src + slen, *dend = dst + dlen, *orig_dst = dst, *p;
                                                ^
frozen.c:949:67: note: Calling function 'json_unescape', 3rd argument 'NULL' value is 0
        int unescaped_len = json_unescape(token->ptr, token->len, NULL, 0);
                                                                  ^
frozen.c:866:49: note: Null pointer addition
  char *send = (char *) src + slen, *dend = dst + dlen, *orig_dst = dst, *p;
                                                ^
frozen.c:561:3: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
  va_copy(ap, xap);
  ^
frozen.c:572:30: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
        int64_t val = va_arg(ap, int64_t);
                             ^
frozen.c:578:29: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
        size_t val = va_arg(ap, size_t);
                            ^
frozen.c:583:43: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
        json_printf_callback_t f = va_arg(ap, json_printf_callback_t);
                                          ^
frozen.c:584:24: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
        len += f(out, &ap);
                       ^
frozen.c:586:26: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
        int val = va_arg(ap, int);
                         ^
frozen.c:592:27: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
        int i, n = va_arg(ap, int);
                          ^
frozen.c:593:41: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
        const unsigned char *p = va_arg(ap, const unsigned char *);
                                        ^
frozen.c:603:41: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
        const unsigned char *p = va_arg(ap, const unsigned char *);
                                        ^
frozen.c:604:24: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
        int n = va_arg(ap, int);
                       ^
frozen.c:615:31: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
          l = (size_t) va_arg(ap, int);
                              ^
frozen.c:618:20: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
        p = va_arg(ap, char *);
                   ^
frozen.c:652:9: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
        va_copy(ap_copy, ap);
        ^
frozen.c:676:13: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
            va_copy(ap_copy, ap);
            ^
frozen.c:696:25: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
          (void) va_arg(ap, int64_t);
                        ^
frozen.c:698:25: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
          (void) va_arg(ap, int);
                        ^
frozen.c:699:25: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
          (void) va_arg(ap, char *);
                        ^
frozen.c:704:29: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
              (void) va_arg(ap, int);
                            ^
frozen.c:741:3: error: va_list 'ap' used before va_start() was called. [va_list_usedBeforeStarted]
  va_end(ap);
  ^
frozen.c:652:9: error: va_list 'ap_copy' used before va_start() was called. [va_list_usedBeforeStarted]
        va_copy(ap_copy, ap);
        ^
frozen.c:653:48: error: va_list 'ap_copy' used before va_start() was called. [va_list_usedBeforeStarted]
        need_len = vsnprintf(pbuf, size, fmt2, ap_copy);
                                               ^
frozen.c:654:9: error: va_list 'ap_copy' used before va_start() was called. [va_list_usedBeforeStarted]
        va_end(ap_copy);
        ^
frozen.c:676:13: error: va_list 'ap_copy' used before va_start() was called. [va_list_usedBeforeStarted]
            va_copy(ap_copy, ap);
            ^
frozen.c:677:49: error: va_list 'ap_copy' used before va_start() was called. [va_list_usedBeforeStarted]
            vsnprintf(pbuf, need_len + 1, fmt2, ap_copy);
                                                ^
frozen.c:678:13: error: va_list 'ap_copy' used before va_start() was called. [va_list_usedBeforeStarted]
            va_end(ap_copy);
            ^
Checking frozen.c: JSON_ENABLE_BASE64...
Checking frozen.c: JSON_ENABLE_HEX...
Checking frozen.c: JSON_MINIMAL=0...
Checking frozen.c: WEAK...
Checking frozen.c: WEAK;_WIN32;__GNUC__;__TI_COMPILER_VERSION__...
Checking frozen.c: _WIN32...
Checking frozen.c: _WIN32;__GNUC__...
1/2 files checked 56% done
Checking unit_test.c ...
frozen.c:812:28: error: Pointer addition with NULL pointer. [nullPointerArithmetic]
  frozen.end = json_string + json_string_length;
                           ^
unit_test.c:122:3: note: Calling function 'json_walk', 1st argument 'NULL' value is 0
  ASSERT(json_walk(NULL, 0, NULL, 0) == JSON_STRING_INVALID);
  ^
frozen.c:812:28: note: Null pointer addition
  frozen.end = json_string + json_string_length;
                           ^
Checking unit_test.c: JSON_ENABLE_BASE64...
Checking unit_test.c: JSON_ENABLE_HEX...
Checking unit_test.c: JSON_MINIMAL=0...
Checking unit_test.c: WEAK...
Checking unit_test.c: WEAK;_WIN32;__GNUC__;__TI_COMPILER_VERSION__...
Checking unit_test.c: _MSC_VER...
Checking unit_test.c: _WIN32...
Checking unit_test.c: _WIN32;__GNUC__...
2/2 files checked 100% done