hotplug_libusb: fix cleanup for IFD_GENERATE_HOTPLUG

If IFD_GENERATE_HOTPLUG is defined by all USB drivers:
    <key>ifdCapabilities</key>
    <string>0x00000001</string>

    <!-- Possible values for ifdCapabilities bits
    1: IFD_GENERATE_HOTPLUG
       plugging the reader calls pcscd \-\-hotplug

    Default value is 0x00000000
    -->

then the hotplug mechanism does not use polling to rescan the USB bus
but waits for pcscd to be called with "--hotplug" to rescan the USB bus
and serial configurations.

This case was not handled correctly on pcscd exit and the
HPEstablishUSBNotifications thread was not terminated.

src/hotplug_libusb.c

@@ -539,6 +539,8 @@ static void * HPEstablishUSBNotifications(int pipefd[2])
  }
  while (read(rescan_pipe[0], &dummy, sizeof(dummy)) > 0)
  {
+ if (AraKiriHotPlug)
+ break;
  Log1(PCSC_LOG_INFO, "Reload serial configuration");
  HPRescanUsbBus();
 #ifdef USE_SERIAL
@@ -597,6 +599,8 @@ LONG HPSearchHotPluggables(const char * hpDirPath)
 LONG HPStopHotPluggables(void)
 {
  AraKiriHotPlug = true;
+ HPReCheckSerialReaders();
+
  if (rescan_pipe[1] >= 0)
  {
  close(rescan_pipe[1]);