KitemListSmoothScroller: delete cloned QWheelEvent after use

Prevent a mem-leak detected with asan.

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This occurs each time we scroll in the view, that could be a very common mem-leak with slow incremental build-up depending on how much scrolling one does...

Candidate for backport.

Indirect leak of 216 byte(s) in 9 object(s) allocated from:
    #0 0x7f63f7920cb5 in malloc (/usr/lib/libasan.so.8+0x120cb5) (BuildId: 0b96d08695bbce2da9d4770c29ad2e72fb536f47)
    #1 0x7f63f02a1f4d in QArrayData::allocate(QArrayData**, long long, long long, long long, QArrayData::AllocationOption) (/usr/lib/libQt6Core.so.6+0x2a1f4d) (BuildId: 951392422ee1339eb724c452dae1a75c8b2c57fc)
    #2 0x7f63f09963e9  (/usr/lib/libQt6Gui.so.6+0x1963e9) (BuildId: d7ee609bd04edf38a36477fc3ff8b7c039ae96f4)
    #3 0x7f63f0984ba3 in QWheelEvent::clone() const (/usr/lib/libQt6Gui.so.6+0x184ba3) (BuildId: d7ee609bd04edf38a36477fc3ff8b7c039ae96f4)
    #4 0x7f63f73a06b9 in KItemListSmoothScroller::handleWheelEvent(QWheelEvent*) /home/meven/kde/src/dolphin/src/kitemviews/private/kitemlistsmoothscroller.cpp:214
    #5 0x7f63f726253c in KItemListContainer::wheelEvent(QWheelEvent*) /home/meven/kde/src/dolphin/src/kitemviews/kitemlistcontainer.cpp:194
    #6 0x7f63f135dc43 in QWidget::event(QEvent*) (/usr/lib/libQt6Widgets.so.6+0x15dc43) (BuildId: 49d09a9a5b72603f589c8d1ee54ae975c822adbe)
    #7 0x7f63f13ccda5 in QFrame::event(QEvent*) (/usr/lib/libQt6Widgets.so.6+0x1ccda5) (BuildId: 49d09a9a5b72603f589c8d1ee54ae975c822adbe)
    #8 0x7f63f016ac49 in QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject*, QEvent*) (/usr/lib/libQt6Core.so.6+0x16ac49) (BuildId: 951392422ee1339eb724c452dae1a75c8b2c57fc)
    #9 0x7f63f130336f in QApplicationPrivate::notify_helper(QObject*, QEvent*) (/usr/lib/libQt6Widgets.so.6+0x10336f) (BuildId: 49d09a9a5b72603f589c8d1ee54ae975c822adbe)
    #10 0x7f63f130542e in QApplication::notify(QObject*, QEvent*) (/usr/lib/libQt6Widgets.so.6+0x10542e) (BuildId: 49d09a9a5b72603f589c8d1ee54ae975c822adbe)
    #11 0x7f63f016bf47 in QCoreApplication::notifyInternal2(QObject*, QEvent*) (/usr/lib/libQt6Core.so.6+0x16bf47) (BuildId: 951392422ee1339eb724c452dae1a75c8b2c57fc)
    #12 0x7f63f137a1ae  (/usr/lib/libQt6Widgets.so.6+0x17a1ae) (BuildId: 49d09a9a5b72603f589c8d1ee54ae975c822adbe)
    #13 0x7f63f130337f in QApplicationPrivate::notify_helper(QObject*, QEvent*) (/usr/lib/libQt6Widgets.so.6+0x10337f) (BuildId: 49d09a9a5b72603f589c8d1ee54ae975c822adbe)
    #14 0x7f63f016bf47 in QCoreApplication::notifyInternal2(QObject*, QEvent*) (/usr/lib/libQt6Core.so.6+0x16bf47) (BuildId: 951392422ee1339eb724c452dae1a75c8b2c57fc)
    #15 0x7f63f09a2dbe in QGuiApplicationPrivate::processWheelEvent(QWindowSystemInterfacePrivate::WheelEvent*) (/usr/lib/libQt6Gui.so.6+0x1a2dbe) (BuildId: d7ee609bd04edf38a36477fc3ff8b7c039ae96f4)
    #16 0x7f63f0a2c3ab in QWindowSystemInterface::sendWindowSystemEvents(QFlags<QEventLoop::ProcessEventsFlag>) (/usr/lib/libQt6Gui.so.6+0x22c3ab) (BuildId: d7ee609bd04edf38a36477fc3ff8b7c039ae96f4)
    #17 0x7f63f0f33cd3  (/usr/lib/libQt6Gui.so.6+0x733cd3) (BuildId: d7ee609bd04edf38a36477fc3ff8b7c039ae96f4)
    #18 0x7f63ec6b5f4c  (/usr/lib/libglib-2.0.so.0+0x5ef4c) (BuildId: e847601b49a0338ea9c34903a2f9d12fcb011e98)
    #19 0x7f63ec6b7616  (/usr/lib/libglib-2.0.so.0+0x60616) (BuildId: e847601b49a0338ea9c34903a2f9d12fcb011e98)
    #20 0x7f63ec6b7824 in g_main_context_iteration (/usr/lib/libglib-2.0.so.0+0x60824) (BuildId: e847601b49a0338ea9c34903a2f9d12fcb011e98)
    #21 0x7f63f044fcb1 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) (/usr/lib/libQt6Core.so.6+0x44fcb1) (BuildId: 951392422ee1339eb724c452dae1a75c8b2c57fc)
    #22 0x7f63f0176cf5 in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) (/usr/lib/libQt6Core.so.6+0x176cf5) (BuildId: 951392422ee1339eb724c452dae1a75c8b2c57fc)
    #23 0x7f63f01709f0 in QCoreApplication::exec() (/usr/lib/libQt6Core.so.6+0x1709f0) (BuildId: 951392422ee1339eb724c452dae1a75c8b2c57fc)
    #24 0x560012c4dcff in main /home/meven/kde/src/dolphin/src/main.cpp:276
    #25 0x7f63efa366c0  (/usr/lib/libc.so.6+0x276c0) (BuildId: 7a8d41a2df4fde040b4c6ac2832311ab645a1e41)
    #26 0x7f63efa367f8 in __libc_start_main (/usr/lib/libc.so.6+0x277f8) (BuildId: 7a8d41a2df4fde040b4c6ac2832311ab645a1e41)
    #27 0x560012c43bc4 in _start (/home/meven/kde/build/dolphin/bin/dolphin+0xecbc4) (BuildId: 1276610ef0598f48aee7e4e4de47a4327b5d680a)