Debugger: Fix crash toggling Stack/"Derefence Pointers" without project

src/plugins/debugger/breakwindow.cpp

src/plugins/debugger/debuggermanager.cpp

src/plugins/debugger/debuggermanager.h

src/plugins/debugger/moduleswindow.cpp

src/plugins/debugger/registerwindow.cpp

src/plugins/debugger/sourcefileswindow.cpp

src/plugins/debugger/stackhandler.cpp

src/plugins/debugger/stackwindow.cpp

src/plugins/debugger/watchwindow.cpp