InputCommon: Fix callback dispatch deadlock

Make sure m_is_populating_devices is true when a WM_INPUT_DEVICE_CHANGE
event is received directly on the ciface thread, so that callbacks do
not occur while removing devices. This breaks a hold-and-wait deadlock
between the ciface thread and the CPU thread when using emulated
Wiimotes.

Co-authored-by: brainleq <brainleq@users.noreply.github.com>
Co-authored-by: oldmud0 <oldmud0@users.noreply.github.com>

Source/Core/InputCommon/ControllerInterface/ControllerInterface.cpp

@@ -140,6 +140,19 @@ void ControllerInterface::RefreshDevices()
   InvokeDevicesChangedCallbacks();
 }
 
+void ControllerInterface::PlatformPopulateDevices(std::function<void()> callback)
+{
+  if (!m_is_init)
+    return;
+
+  m_is_populating_devices = true;
+
+  callback();
+
+  m_is_populating_devices = false;
+  InvokeDevicesChangedCallbacks();
+}
+
 // Remove all devices and call library cleanup functions
 void ControllerInterface::Shutdown()
 {