Revert part of the commit 12a0837

I forgot I have designed "Keep the client active" for issue #22
isBusy() is deprecated for blocking the port, but it doesn't matter.

common/pm3process.cpp

@@ -107,15 +107,15 @@ void PM3Process::setSerialListener(bool state)
 
 void PM3Process::onTimeout() //when the proxmark3 client is unexpectedly terminated or the PM3 hardware is removed, the isBusy() will return false(only tested on Windows);
 {
-//    isBusy() is a deprecated function.
-//    It will always return false on Raspbian.
-//    SerialListener needs to be removed.
+//    isBusy() is a deprecated function because it will block the serial port when the port is not in use.
+//    However, the PM3 client is supposed to use the serial port exclusively, so it should be fine
+//    isBusy() will always return false on Raspbian, in this case, check "Keep the client active" in the Settings panel.
 //
 //    qDebug()<<portInfo->isBusy();
-//    if(!portInfo->isBusy())
-//    {
-//        killPM3();
-//    }
+    if(!portInfo->isBusy())
+    {
+        killPM3();
+    }
 }
 
 void PM3Process::testThread()

ui/mainwindow.ui

@@ -2833,7 +2833,7 @@ or &quot;-p &lt;port&gt; -f&quot;</string>
                   </sizepolicy>
                  </property>
                  <property name="text">
-                  <string>Keep te client active even the PM3 hardware is disconnected.(Experimental)</string>
+                  <string>Keep the client active even the PM3 hardware is disconnected.(Experimental)</string>
                  </property>
                  <property name="wordWrap">
                   <bool>true</bool>