gr-osmosdr setting value in destructor

[P]

Hi,

there is in gr-osmosdr a lot of code like:

hackrf_source_c::~hackrf_source_c ()
{
...
    free(_buf);
    _buf = NULL;
  }
}

Setting value in destructor have sense in two case:
  - they are used in some way in destructor of parent class
  - You set then to something like 0xDEADBEEF and when pointer
    from already destroyed class is used it will cause segfault.

Setting value to NULL is contraproductive because there is a lot of
checks if value is not NULL, this actually can hide some troubles of
calling something using already freed pointer.

I'm suggesting to remove this kind of code. I will prepare patch but now
I'm waiting if those two pending patches I have send before would be
accepter or not.

Is there any opinion which oppose previous claim?

With best regards,
	JP.