emscripten: Fixed return type in event callback declaration.

src/video/emscripten/SDL_emscriptenevents.h

@@ -31,8 +31,9 @@ Emscripten_RegisterEventHandlers(SDL_WindowData *data);
 extern void
 Emscripten_UnregisterEventHandlers(SDL_WindowData *data);
 
-extern int
+extern EM_BOOL
 Emscripten_HandleCanvasResize(int eventType, const void *reserved, void *userData);
+
 #endif /* _SDL_emscriptenevents_h */
 
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