macosx: fixed crash when terminating while the progress panel is displayed

(cherry picked from commit 6c62d7475dce83cbc116f4bcc470ee4f9078e6c1)

Conflicts:
	modules/gui/macosx/intf.m

modules/gui/macosx/intf.m

@@ -449,7 +449,10 @@ void updateProgressPanel (void *priv, const char *text, float value)
 void destroyProgressPanel (void *priv)
 {
     NSAutoreleasePool *o_pool = [[NSAutoreleasePool alloc] init];
-    [[[VLCMain sharedInstance] coreDialogProvider] destroyProgressPanel];
+
+    if ([[NSApplication sharedApplication] isRunning])
+        [[[VLCMain sharedInstance] coreDialogProvider] performSelectorOnMainThread:@selector(destroyProgressPanel) withObject:nil waitUntilDone:YES];
+
     [o_pool release];
 }