fixed import_image not generating in CLI

src/gfx/generated_image.hpp

@@ -408,6 +408,7 @@ public:
     Image generate(const Options&) const override;
     bool operator == (const GeneratedImage& that) const override;
     inline String toString() { return filepath; }
+    inline String ExternalImage::toCode() const override { return "<image>"; }
 private:
     String filepath;
 };