Guard against null dereference on missing/non-numeric "state" field in GetWifiState JSON parsing

[Copilot]

Accessing state->valueint in the GetWifiState block had no null or type check — if the JSON response omitted "state" or returned it as a non-numeric type, the code would dereference a null pointer.

Changes

• Device_WiFi_SSID.cpp: Added !state || !cJSON_IsNumber(state) guard immediately after cJSON_GetObjectItem(jsonObj, "state"), before any access to state->valueint. Returns NOK with an error log on failure.

cJSON *state = cJSON_GetObjectItem(jsonObj, "state");
if (!state || !cJSON_IsNumber(state))
{
    RDK_LOG(RDK_LOG_ERROR, LOG_TR69HOSTIF,
            "[%s] json parse error, \"state\" field missing or not a number\n", __FUNCTION__);
    cJSON_Delete(root);
    return NOK;
}
int res = state->valueint;

Consistent with the validation pattern used for "state" in Device_WiFi_EndPoint.cpp.

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