add iOS and macOS icons

src/asset.cpp

@@ -33,8 +33,11 @@ bool Asset::exist(std::string path)
     }
     else
     {
-        std::ifstream f(path, std::ios::binary);
-        return f.is_open();
+        FILE* fp = fopen(path.c_str(), "rb");
+        if (!fp)
+            return false;
+        fclose(fp);
+        return true;
     }
     return false; // useless return for the stupid xcode 
 }