Initialize meshPoints_ to null pointers

[vidulejs]

Fixed bug where storeMeshPoints() would not store points because meshPoints_ pointer had garbage non-zero value.

// Adapter.C
void preciceAdapter::Adapter::storeMeshPoints()
{
    if (!meshPoints_)
    {
        DEBUG(adapterInfo("Storing mesh points..."));
        // Add points and oldPoints
        meshPoints_ = new Foam::pointField(mesh_.points());
        meshOldPoints_ = new Foam::pointField(mesh_.oldPoints());
    }
    //... 

The fix was to initialize with null pointers:

// Adapter.H
    //- Checkpointed mesh points, oldPoints
    Foam::pointField* meshPoints_ = NULL;
    Foam::pointField* meshOldPoints_ = NULL;

TODO list:

• I updated the documentation in docs/
• I added a changelog entry in changelog-entries/ (create directory if missing)

[MakisH]

Merging to get the system tests working again. I can update the rest of the pointers in another PR.