Suppress idle keyswitch events from virtual hardware device

The virtual hardware device, unlike others, was calling `handleKeyswitchEvent()`
for every keyswitch, every cycle. It should suppress calls corresponding to idle
keyswitches, just like the other devices.

Signed-off-by: Michael Richters <gedankenexperimenter@gmail.com>

src/kaleidoscope/device/virtual/Virtual.cpp

@@ -260,6 +260,7 @@ void VirtualKeyScanner::actOnMatrixScan() {
       break;
     }
 
+    if (key_state != 0)
       handleKeyswitchEvent(Key_NoKey, key_addr, key_state);
     keystates_prev_[key_addr.toInt()] = keystates_[key_addr.toInt()];