terminal: fix nil pointer dereference in pty.Getsize

pty.Getsize() is used in the Draw function of the terminal widget and wraps the
pty.GetsizeFull() function. However, pty.Getsize does not check the returned
error from pty.GetsizeFull before dereferencing the winsize struct. In case of
an error, this will cause a nil pointer deference and panic.

This has been reported in the upstream package, but in the meantime, we can
directly use pty.GetsizeFull.

References: https://todo.sr.ht/~rjarry/aerc/11
Signed-off-by: Koni Marti <koni.marti@gmail.com>

widgets/terminal.go

@@ -254,10 +254,13 @@ func (term *Terminal) Draw(ctx *ui.Context) {
 			}
 		}
 
-		rows, cols, err := pty.Getsize(term.pty)
+		ws, err := pty.GetsizeFull(term.pty)
 		if err != nil {
 			return
 		}
+		rows := int(ws.Rows)
+		cols := int(ws.Cols)
+
 		if ctx.Width() != cols || ctx.Height() != rows {
 			term.writeMutex.Lock()
 			pty.Setsize(term.pty, &winsize)