clear pending stream outputs after handling stop response

any output will most definitely belong to later issued commands, so not
clearing it will only cost cpu or even confuse the evaluation.

Reviewed-by: hjk

src/plugins/debugger/gdb/gdbengine.cpp

@@ -427,6 +427,8 @@ void GdbEngine::handleResponse(const QByteArray &buff)
             }
             if (asyncClass == "stopped") {
                 handleStopResponse(result);
+                m_pendingLogStreamOutput.clear();
+                m_pendingConsoleStreamOutput.clear();
             } else if (asyncClass == "running") {
                 // Archer has 'thread-id="all"' here
             } else if (asyncClass == "library-loaded") {