wasm: don’t exit on clean return from main()

Qt 6 uses Emcripten’s default of not exiting the runtime
when main() exits. Make qtloader not transition to
the “Exited” state when main() exits with code 0, since
this would hide the app canvas.

(The app state tracking code in qtloader is by now
outdated, and should be revisited.)

Pick-to: 6.3
Change-Id: Ib47898f1dd93d87b2675f20cd39f96ac3cb681a7
Reviewed-by: David Skoland <david.skoland@qt.io>
Reviewed-by: Lorn Potter <lorn.potter@gmail.com>

src/plugins/platforms/wasm/qtloader.js

@@ -407,6 +407,12 @@ function QtLoader(config)
             setStatus("Exited");
         };
         self.moduleConfig.quit = self.moduleConfig.quit || function(code, exception) {
+
+            // Emscripten (and Qt) supports exiting from main() while keeping the app
+            // running. Don't transition into the "Exited" state for clean exits.
+            if (code == 0)
+                return;
+
             if (exception.name == "ExitStatus") {
                 // Clean exit with code
                 publicAPI.exitText = undefined