bugfix: initial textinput event on iOS

`love.textinput` is fragile on iOS. Various things can cause an app to
stop receiving textinput events. Resizing the window is one reliable
way, but there's also another ghost, something that's triggering on
every frame of LÖVE.

Fortunately, it looks like `love.keyboard.setTextInput(true)` reliably
resubscribes the app to textinput events, regardless of their cause.

https://github.com/love2d/love/issues/1959

The one remaining open question here is why the call in
`App.keychord_press` (equivalent to `love.keypressed`) doesn't fix the
breakage caused by the initial window resize (that happens before any
keys are pressed). I've confirmed that `keypressed` comes before
`textinput` on iOS just like everywhere else.

app.lua

@@ -68,7 +68,15 @@ function love.run()
   App.fake_mouse_press = nil
   App.fake_mouse_release = nil
   -- other methods dispatch to real hardware
-  App.screen.resize = love.window.setMode
+
+  App.screen.resize = function(width, height, flags)
+    love.window.setMode(width, height, flags)
+    if OS == 'iOS' then
+      love.keyboard.setTextInput(true)  -- magic. iOS seems to lose textinput events after calls to setMode.
+                                        -- https://github.com/love2d/love/issues/1959
+    end
+  end
+
   App.screen.size = love.window.getMode
   App.screen.move = love.window.setPosition
   App.screen.position = love.window.getPosition

main.lua

@@ -1,6 +1,8 @@
 utf8 = require 'utf8'
 json = require 'json'
 
+OS = love.system.getOS()
+
 require 'app'
 require 'test'
 require 'live'
@@ -8,8 +10,6 @@ require 'live'
 require 'keychord'
 require 'button'
 
-OS = love.system.getOS()
-
 -- delegate most business logic to a layer that can be reused by other projects
 require 'edit'
 Editor_state = {}
@@ -216,7 +216,10 @@ function App.keychord_press(chord, key)
     end
     return
   end
-  love.keyboard.setTextInput(true)  -- magic. keeps iOS from losing textinput events after switching apps.
+  if OS == 'iOS' then
+    love.keyboard.setTextInput(true)  -- magic. iOS is prone to losing textinput events.
+                                      -- https://github.com/love2d/love/issues/1959
+  end
   -- ignore events for some time after window in focus (mostly alt-tab)
   if Current_time < Last_focus_time + 0.01 then
     return