Debugger: Clean pending lookup requests when preparing a step

This avoids accumulating lookup requests when stepping quickly.
They won't produce usable output anymore.

Change-Id: I9e29ca1778019e3eab37d122386d3faf0e07edbf
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>

src/plugins/debugger/qml/qmlengine.cpp

@@ -768,6 +768,12 @@ void QmlEngine::insertBreakpoint(Breakpoint bp)
     d->breakpointsSync.insert(d->sequence, bp.id());
 }
 
+void QmlEngine::resetLocation()
+{
+    DebuggerEngine::resetLocation();
+    d->currentlyLookingUp.clear();
+}
+
 void QmlEngine::removeBreakpoint(Breakpoint bp)
 {
     const BreakpointParameters &params = bp.parameters();

src/plugins/debugger/qml/qmlengine.h

@@ -80,6 +80,8 @@ private:
     bool isSynchronous() const override { return false; }
     bool canDisplayTooltip() const override { return false; }
 
+    void resetLocation() override;
+
     void executeStep() override;
     void executeStepOut() override;
     void executeNext() override;