Set bar_size to nil in progress_bar again

See the lengthy comment to learn why

init.lua

@@ -228,7 +228,13 @@ function hb.register_hudbar(identifier, text_color, label, textures, default_sta
 		local bar_image, bar_size
 		if hb.settings.bar_type == "progress_bar" then
 			bar_image = textures.bar
-			bar_size = {x=2, y=16}
+			-- NOTE: Intentionally set to nil. For some reason, on some systems,
+			-- the progress bar is displaced when the bar_size is set explicitly here.
+			-- On the other hand, setting this to nil is deprecated in MT 5.0.0 due to
+			-- a debug log warning, but nothing is explained in lua_api.txt.
+			-- This section is a potential bug magnet, please watch with care!
+			-- The size of the bar image is expected to be exactly 2×16 pixels.
+			bar_size = nil
 		elseif hb.settings.bar_type == "statbar_classic" or hb.settings.bar_type == "statbar_modern" then
 			bar_image = textures.icon
 			bar_size = {x=24, y=24}