[C][Client] Fix the memory leak when a JSON of model fails to parse

[ityuhui]

The function *_parseFromJSON()
e.g. pet_t *pet_parseFromJSON(cJSON *petJSON) creates and returns a model pet_t according to the parameter cJSON *petJSON.

If petJSON is not a valid cJSON for pet_t, the function pet_parseFromJSON can not create the model pet_t successfully, and return NULL directly. At this time, some parts of pet_t have been created, e.g. category_local_nonprim, but the function forgets to release its memory, this will cause memory leak.

This PR fixes this memory leak via deleting the memory before return NULL

This PR only covers the type of isModel/complexType for the member of model, does not cover other types e.g. isArray, isFreeFormObject, isMap because now I only have the use case of isModel/complexType. We can fix other types when we meet them in future.

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@wing328 @zhemant @michelealbano

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