Don't allow seeking below 0 (unexpected behavior)

src/monitor/monitor.cpp

@@ -1173,7 +1173,7 @@ void Monitor::slotForward(double speed)
 void Monitor::slotRewindOneFrame(int diff)
 {
     slotActivateMonitor();
-    m_glMonitor->getControllerProxy()->setPosition(m_glMonitor->getCurrentPos() - diff);
+    m_glMonitor->getControllerProxy()->setPosition(qMax(0, m_glMonitor->getCurrentPos() - diff));
 }
 
 void Monitor::slotForwardOneFrame(int diff)

src/timeline2/view/qml/timeline.qml

@@ -892,7 +892,7 @@ Rectangle {
                     }
                 } else {
                     var delta = wheel.modifiers & Qt.ShiftModifier ? timeline.fps() : 1
-                    proxy.position = Math.min(root.consumerPosition - (wheel.angleDelta.y > 0 ? delta : -delta), timeline.fullDuration - 1)
+                    proxy.position = wheel.angleDelta.y > 0 ? Math.max(root.consumerPosition - delta, 0) : Math.min(root.consumerPosition + delta, timeline.fullDuration - 1)
                 }
             }
             onPressed: {