monitor-utils: clear cam data after creating nodes

The cam_data structure stores a reference to the "parent" WpSpaDevice
and doesn't allow it to be destroyed when the monitor detects that
the device is no longer present. Clear it right after pushing the event
to make sure there's no dangling reference left around

Fixes: #627

src/scripts/lib/monitor-utils.lua

@@ -40,6 +40,15 @@ function mutils.get_cam_data (self, dev_string)
   return self.cam_data[dev_num], dev_num
 end
 
+function mutils.clear_cam_data (self, dev_string)
+  local dev_num = tonumber (dev_string)
+  if not dev_num then
+    return
+  end
+
+  self.cam_data[dev_num] = nil
+end
+
 function mutils.create_cam_node (self, dev_num)
   local api = nil
   local cam_data = self:get_cam_data (dev_num)
@@ -65,6 +74,8 @@ function mutils.create_cam_node (self, dev_num)
   e:set_data ("node-sub-id", cam_data[api].id)
 
   EventDispatcher.push_event (e)
+
+  self:clear_cam_data (dev_num)
 end
 
 -- arbitrates between v4l2 and libcamera on who gets to create the device node