Work around 0.15.22 bug with disappearing GUIs

As per the comment in the source, if a mod creates a GUI element whose
name is both:
  - longer than 4 characters, and
  - less than 4 characters longer than the mod name,
the element would be considered to belong to a mod that isn't present
and get removed.

We fixed this earlier in its guise as #71, which is how the bug appears
in single-player, but in multiplayer the removal runs only client-side
on joining, causing an instant desync for the joining player.

My workaround is to rename the root element to evogui_root and hope
(suspect, believe) that the remaining GUI elements all have longer names
or won't cause instant breakage (so far, this seems to be holding).

On the other hand, updating just EvoGUI while still on Factorio 0.15.22
needs to be a two-step process: save the game once, *then* reload it
(start server, stop server, start server), as otherwise the client will
cause the same desync again. It's possible just waiting until the first
server autosave may also fix it, but it's quicker this way.

Closes #74.

VERSION

@@ -1 +1 @@
-0.4.204
+0.4.205

evoGUI.lua

@@ -20,12 +20,32 @@ function evogui.mod_init()
     end
 end
 
+
+local function mod_update_0_4_205()
+    -- 0.4.204 to 0.4.205: Factorio 0.15.22 introduced a bug wherein a
+    -- GUI element with more than 4 characters in its name, which was
+    -- shorter than the_mod_name + 4 characters, would get deleted on
+    -- load. At this time, the EvoGUI root element switched from
+    -- gui.top.evoGUI to gui.top.evogui_root.
+    --
+    -- We need to clean up the leftovers for people updating EvoGUI
+    -- from any other version of Factorio now.
+    for _, player in pairs(game.players) do
+        if player.gui.top.evoGUI then
+            player.gui.top.evoGUI.destroy()
+        end
+    end
+end
+
+
 function evogui.mod_update(data)
     if data.mod_changes then
         if data.mod_changes["{{MOD_NAME}}"] then
             -- TODO: If a more major migration ever needs doing, do that here.
             -- Otherwise, just falling back to mod_init should work fine.
             evogui.mod_init()
+
+            mod_update_0_4_205()
         end
 
         evogui.validate_sensors(data.mod_changes)
@@ -72,7 +92,7 @@ function evogui.hide_sensor(sensor)
     for _, player in pairs(game.players) do
         local player_settings = global.evogui[player.name]
 
-        local sensor_flow = player.gui.top.evoGUI.sensor_flow
+        local sensor_flow = player.gui.top.evogui_root.sensor_flow
         evogui.update_av(player, sensor_flow.always_visible)
     end
 end
@@ -96,11 +116,11 @@ function evogui.update_gui(event)
         if not player_settings then
             evogui.new_player({player_index = player_index})
             player_settings = global.evogui[player.name]
-        elseif not player.gui.top.evoGUI then
+        elseif not player.gui.top.evogui_root then
             evogui.create_sensor_display(player)
         end
 
-        local sensor_flow = player.gui.top.evoGUI.sensor_flow
+        local sensor_flow = player.gui.top.evogui_root.sensor_flow
         evogui.update_av(player, sensor_flow.always_visible)
         if player_settings.popup_open then
             evogui.update_ip(player, sensor_flow.in_popup)
@@ -171,16 +191,16 @@ end
 
 
 function evogui.create_sensor_display(player)
-    local root = player.gui.top.evoGUI
+    local root = player.gui.top.evogui_root
     local destroyed = false
     if root then
-        player.gui.top.evoGUI.destroy()
+        player.gui.top.evogui_root.destroy()
         destroyed = true
     end
 
     if not root or destroyed then
         local root = player.gui.top.add{type="frame",
-                                        name="evoGUI",
+                                        name="evogui_root",
                                         direction="horizontal",
                                         style="outer_frame_style"}
 
@@ -249,7 +269,7 @@ function evogui.evoGUI_toggle_popup(event)
     local player = game.players[event.player_index]
     local player_settings = global.evogui[player.name]
 
-    local root = player.gui.top.evoGUI
+    local root = player.gui.top.evogui_root
 
     if player_settings.popup_open then
         -- close it