(draw_monitor) fix crash (#33023)

However, there's a race window on "gtkflush() while $isconnected == -2
|| $isconnected == -1" where net_monitor can continue executing
(with an empty window):

Gtk-CRITICAL **: gtk_main_quit: assertion `main_loops != NULL' failed at
/usr/lib/libDrakX/mygtk2.pm line 915.
kid exited -1 at /usr/lib/libDrakX/run_program.pm line 167.
Gtk-CRITICAL **: gtk_label_set_text: assertion `GTK_IS_LABEL (label)' failed at
./bin/net_monitor line 468.
Gtk-CRITICAL **: gtk_label_set_text: assertion `GTK_IS_LABEL (label)' failed at
./bin/net_monitor line 469.

1 files changed, 3 insertions, 0 deletions

diff --git a/bin/net_monitor b/bin/net_monitor
index b9ca3de..a93fea2 100755
--- a/bin/net_monitor
+++ b/bin/net_monitor
@@ -486,6 +486,9 @@ sub draw_monitor {
     defined $darea->{$intf} or return;
     my $gcl = $gc_lines->{$intf};
     my $pixmap = $pixmap->{$intf};
+    my $gc = $darea->{$intf}->style->white_gc;
+    # fix race on ugtk2->exit that causes a crash (#33023)
+    return 0 if !$gc;
     $pixmap->draw_rectangle($darea->{$intf}->style->black_gc, 1, 0, 0, $width, $height);
     my $maxr = 0;
     foreach (@{$o->{stack_r}}) { $maxr = $_ if $_ > $maxr }