clean up output printing in dumpBacktrace()

the first call to readAllStandardOutput() made no sense, as the buffer
would be empty at that time anyway.

Change-Id: Ie306745a94f98ce358e4af373169d0a5b0a82d23
Reviewed-by: hjk <hjk@qt.io>

src/plugins/debugger/shared/backtrace.cpp

@@ -55,12 +55,10 @@ void dumpBacktrace(int maxdepth)
     for (int i = 0; i < qMin(size, maxdepth); i++)
         proc.write("0x" + QByteArray::number(quintptr(bt[i]), 16) + '\n');
     proc.closeWriteChannel();
+    proc.waitForFinished();
     QByteArray out = proc.readAllStandardOutput();
     qDebug() << QCoreApplication::arguments().at(0);
     qDebug() << out;
-    proc.waitForFinished();
-    out = proc.readAllStandardOutput();
-    qDebug() << out;
 #endif
 }