call: Initialize m_pParentCall using C++11 paradigm

Minor one. Call has multiple constructor and all of them init
the pointer to nullptr in the constructor body. Still enough
to fire a CI warning.

Change-Id: Ia1a9c532262cf6b1b28dc1bd95090a4d54bcb4da

src/call.cpp

@@ -317,7 +317,6 @@ Call::Call(Call::State startState, const QString& peerName, ContactMethod* numbe
    d_ptr->m_Account          = account;
    d_ptr->m_PeerName         = peerName;
    d_ptr->m_pPeerContactMethod = number;
-   d_ptr->m_pParentCall      = nullptr;
 
    emit changed();
 }
@@ -331,7 +330,6 @@ Call::Call(const QString& confId, const QString& account)
    d_ptr->m_Account      = AccountModel::instance().getById(account.toLatin1());
    d_ptr->m_Type         = (!confId.isEmpty())?Call::Type::CONFERENCE:Call::Type::CALL;
    d_ptr->m_DringId      = confId;
-   d_ptr->m_pParentCall  = nullptr;
 
    setObjectName("Conf:"+confId);
 

src/private/call_p.h

@@ -126,7 +126,7 @@ public:
    Call::Type                m_Type              ;
    Certificate*              m_pCertificate      ;
    FlagPack<Call::HoldFlags> m_fHoldFlags        ;
-   Call*                     m_pParentCall       ;
+   Call*                     m_pParentCall {nullptr};
    QDateTime*                m_pDateTime {nullptr};
    QDate*                    m_pDateOnly {nullptr};
    QString                   m_FormattedDate     ;