Debugger: Don't retrieve full stack on frame switch with LLDB

Unneeded effort and also re-sets the marker to the top frame
somewhat spoiling part of the result.

Change-Id: Iebaa52dc8c0703f3245cac2ca15b942e3006993a
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>

src/plugins/debugger/lldb/lldbengine.cpp

@@ -519,7 +519,8 @@ void LldbEngine::activateFrame(int frameIndex)
     cmd.arg("thread", threadsHandler()->currentThread().raw());
     runCommand(cmd);
 
-    updateAll();
+    reloadRegisters();
+    updateLocals();
 }
 
 void LldbEngine::selectThread(ThreadId threadId)