Debugger: Fix enabling breakpoints on click

Calling `BreakpointItem::setEnabled` from `BreakpointMarker::clicked` is
wrong and dangerous. It never actually enables a global breakpoint,
just updates the marker. While doing so, it calls
`BreakpointItem::adjustMarker`, which in turn calls
`BreakpointItem::destroyMarker`, which destroys the original marker,
hence the dangerous part.

What we actually want is simply enable the corresponding global
breakpoint instead.

Amends 8f3a0ebabb.

Change-Id: I423752be4e4f51198e9e2968a978b57bce43a3ec
Reviewed-by: hjk <hjk@qt.io>

src/plugins/debugger/breakhandler.cpp

@@ -120,10 +120,14 @@ public:
     void clicked() final
     {
         QTC_ASSERT(m_bp, return);
-        if (!m_bp->isEnabled())
-            m_bp->setEnabled(true);
-        else
+
+        if (m_bp->isEnabled()) {
             m_bp->deleteGlobalOrThisBreakpoint();
+            return;
+        }
+
+        if (const GlobalBreakpoint gbp = m_bp->globalBreakpoint())
+            gbp->setEnabled(true);
     }
 
 public: