Revert "thread: Close channels"

This reverts commit 00e78c1eae.

Reason: (*Thread).Loop can be called multiple times on iOS.

Fixes #1121

internal/thread/thread.go

@@ -22,7 +22,6 @@ import (
 type Thread struct {
 	funcs   chan func() error
 	results chan error
-	closed  chan struct{}
 }
 
 // New creates a new thread.
@@ -32,7 +31,6 @@ func New() *Thread {
 	return &Thread{
 		funcs:   make(chan func() error),
 		results: make(chan error),
-		closed:  make(chan struct{}),
 	}
 }
 
@@ -40,9 +38,6 @@ func New() *Thread {
 //
 // Loop must be called on the thread.
 func (t *Thread) Loop(context context.Context) {
-	defer close(t.closed)
-	defer close(t.results)
-	defer close(t.funcs)
 loop:
 	for {
 		select {
@@ -60,10 +55,6 @@ loop:
 //
 // Call panics when Loop already ends.
 func (t *Thread) Call(f func() error) error {
-	select {
-	case t.funcs <- f:
-		return <-t.results
-	case <-t.closed:
-		panic("thread: this thread is already terminated")
-	}
+	t.funcs <- f
+	return <-t.results
 }