Fixup getting the right main thread ID for mobile

internal/async/goroutine.go

@@ -10,12 +10,11 @@ import (
 )
 
 // mainGoroutineID stores the main goroutine ID.
-// This ID must be initialized in main.init because
-// a main goroutine may not equal to 1 due to the
-// influence of a garbage collector.
+// This ID must be initialized during setup by calling `SetMainGoroutine` because
+// a main goroutine may not equal to 1 due to the influence of a garbage collector.
 var mainGoroutineID uint64
 
-func init() {
+func SetMainGoroutine() {
 	mainGoroutineID = goroutineID()
 }
 

internal/driver/glfw/loop.go

@@ -28,6 +28,7 @@ var initOnce = &sync.Once{}
 // Arrange that main.main runs on main thread.
 func init() {
 	runtime.LockOSThread()
+	async.SetMainGoroutine()
 }
 
 // force a function f to run on the main thread

internal/driver/mobile/driver.go

@@ -74,6 +74,10 @@ func init() {
 
 func (d *driver) DoFromGoroutine(fn func(), wait bool) {
 	async.EnsureNotMain(func() {
+		if d.queuedFuncs == nil {
+			fn() // before the app actually starts
+			return
+		}
 		var done chan struct{}
 		if wait {
 			done = common.DonePool.Get()
@@ -167,6 +171,7 @@ func (d *driver) Run() {
 	d.running = true
 
 	app.Main(func(a app.App) {
+		async.SetMainGoroutine()
 		d.app = a
 		settingsChange := make(chan fyne.Settings)
 		d.queuedFuncs = async.NewUnboundedChan[func()]()