FileChooser: Fix behaviour of macOS FilePreviewComponent

Previously, when the FileChooser::Native instance entered the
modal state, it was preventing the inner FilePreviewComponent from
receiving events.

modules/juce_gui_basics/native/juce_mac_FileChooser.mm

@@ -97,11 +97,11 @@ public:
         if (preview != nullptr)
         {
             nsViewPreview = [[NSView alloc] initWithFrame: makeNSRect (preview->getLocalBounds())];
+            [panel setAccessoryView: nsViewPreview];
+
             preview->addToDesktop (0, (void*) nsViewPreview);
             preview->setVisible (true);
 
-            [panel setAccessoryView: nsViewPreview];
-
             if (! isSave)
             {
                 auto* openPanel = static_cast<NSOpenPanel*> (panel);
@@ -187,6 +187,9 @@ public:
         if (targetComponent == nullptr)
             return false;
 
+        if (targetComponent == preview)
+            return true;
+
         return targetComponent->findParentComponentOfClass<FilePreviewComponent>() != nullptr;
     }