Avoid nullptr access

[ivannp]

Merely loading libdds.so on Ubuntu crashes the parent program on exit. To repro, run the following python command:

python -c 'from ctypes import *; dll = CDLL("libdds.so");'

I chased it down to trying to release memory on exit. It looks like the logic behind freeing the memory is broken, when the thread count is less than what's in the array. One might argue that this fix fixes the symptom, but it's better to avoid accessing pointers blindly.

This fix fixes the problem only on 18.04. On 16.04 it seems we are hitting the following line from Memory.cpp:

cout << "Memory::GetPtr: " << thrId << " vs. " << nThreads << endl;

From a quick inspection of the code, I expect to be similar issue. Haven't spent the time debugging it yet.

[t3nsor]

I think the code that determines the amount of free memory (Memory.cpp:228) may be the issue. On my system (Debian 9) it produces 0. Note that the full output of free -k for me is:

          total        used        free      shared  buff/cache   available

Mem: 16198028 5259516 808524 173588 10129988 10428852
Swap: 0 0 0

The output format was changed about 4 years ago: https://gitlab.com/procps-ng/procps/commit/f47001c9e91a1e9b12db4497051a212cf49a87b1

[df7cb]

See #88.

[sorenhein]

Thanks. It did fix your issue, but it seems that rimmington fixed some larger issues that included yours, so I've gone with his pull request.