fix: detect terminal size after exec

Based on @knz's work in #499, but slightly supersedes this change.

A little more coupling in the resize handling, but a lot less code
& logic repetition.

Co-authored-by: Raphael 'kena' Poss <knz@thaumogen.net>

signals_unix.go

@@ -4,18 +4,15 @@
 package tea
 
 import (
-	"context"
 	"os"
 	"os/signal"
 	"syscall"
-
-	"golang.org/x/term"
 )
 
 // listenForResize sends messages (or errors) when the terminal resizes.
 // Argument output should be the file descriptor for the terminal; usually
 // os.Stdout.
-func listenForResize(ctx context.Context, output *os.File, msgs chan Msg, errs chan error, done chan struct{}) {
+func (p *Program) listenForResize(done chan struct{}) {
 	sig := make(chan os.Signal, 1)
 	signal.Notify(sig, syscall.SIGWINCH)
 
@@ -26,20 +23,11 @@ func listenForResize(ctx context.Context, output *os.File, msgs chan Msg, errs c
 
 	for {
 		select {
-		case <-ctx.Done():
+		case <-p.ctx.Done():
 			return
 		case <-sig:
 		}
 
-		w, h, err := term.GetSize(int(output.Fd()))
-		if err != nil {
-			errs <- err
-		}
-
-		select {
-		case <-ctx.Done():
-			return
-		case msgs <- WindowSizeMsg{w, h}:
-		}
+		p.checkResize()
 	}
 }