Explicitly exit cleanup process

This avoids an internal crash reported in `adb logcat`.

Refs #4456 <https://github.com/Genymobile/scrcpy/pull/4456#issuecomment-1837427802>

server/src/main/java/com/genymobile/scrcpy/CleanUp.java

@@ -187,5 +187,7 @@ public final class CleanUp {
                 Device.setScreenPowerMode(Device.POWER_MODE_NORMAL);
             }
         }
+
+        System.exit(0);
     }
 }