[C][Client] Define and initialize non-primitive variables at the beginning of function

Created by: ityuhui

In the functions *_parseFromJSON of the generated C-libcurl client code, when an error occurs, all the non-primitive variables will be freed before the function exits. e.g.

pet_t *pet_parseFromJSON(cJSON *petJSON){
...
    // pet->id
    cJSON *id = cJSON_GetObjectItemCaseSensitive(petJSON, "id");
    if (id) { 
        if(!cJSON_IsNumber(id))
        {
            goto end; //Numeric
        }
    }

    // pet->category
    cJSON *category = cJSON_GetObjectItemCaseSensitive(petJSON, "category");
    category_t *category_local_nonprim = NULL;
...

end:
    if (category_local_nonprim) {
        category_free(category_local_nonprim);
        category_local_nonprim = NULL;
    }
    return NULL;
}

But sometimes, the variables are not defined and initialized at this time. e.g. category_local_nonprim is not defined if id is invalid. Freeing category_local_nonprim will cause core-dump.

The fix solution is to define and initialize non-primitive variables at the beginning of function.

e.g.

pet_t *pet_parseFromJSON(cJSON *petJSON){

    // define the local varable for pet->category
    category_t *category_local_nonprim = NULL;

    // pet->id
    cJSON *id = cJSON_GetObjectItemCaseSensitive(petJSON, "id");
    if (id) { 
        if(!cJSON_IsNumber(id))
        {
            goto end; //Numeric
        }
    }

    // pet->category
    cJSON *category = cJSON_GetObjectItemCaseSensitive(petJSON, "category");
...
}

Hi @wing328 @zhemant @michelealbano

Could you please review this PR ? Thanks !

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