Initialize m_konsolePartMissingMessage

Otherwise it just crashes when trying to open the terminal panel

BUG: 392660
Differential Revision: https://phabricator.kde.org/D11904

src/panels/terminal/terminalpanel.cpp

@@ -47,6 +47,7 @@ TerminalPanel::TerminalPanel(QWidget* parent) :
     m_layout(nullptr),
     m_terminal(nullptr),
     m_terminalWidget(nullptr),
+    m_konsolePartMissingMessage(nullptr),
     m_konsolePart(nullptr),
     m_konsolePartCurrentDirectory(),
     m_sendCdToTerminalHistory()