git-gui: Fix the blame viewer destroy handler.

It did not delete the object, which is not very good.
Also, destroy may be fired up for subwindows, so we
should check %W.

Signed-off-by: Alexander Gavrilov <angavrilov@gmail.com>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

lib/blame.tcl

@@ -377,11 +377,18 @@ constructor new {i_commit i_path i_jump} {
 	"if {{$w.file_pane} eq {%W}} {[cb _resize %h]}"
 
 	wm protocol $top WM_DELETE_WINDOW "destroy $top"
-	bind $top <Destroy> [cb _kill]
+	bind $top <Destroy> [cb _handle_destroy %W]
 
 	_load $this $i_jump
 }
 
+method _handle_destroy {win} {
+	if {$win eq $w} {
+		_kill $this
+		delete_this
+	}
+}
+
 method _kill {} {
 	if {$current_fd ne {}} {
 		kill_file_process $current_fd