Allow using an Fl_SVG_Image object as window icon.

Fix for issue #90: Setting an svg image as a window icon causes a segfault.

FL/Fl_Image.H

@@ -273,6 +273,7 @@ public:
   static bool register_images_done;
 };
 
+class Fl_SVG_Image;
 
 /**
   The Fl_RGB_Image class supports caching and drawing
@@ -291,6 +292,7 @@ class FL_EXPORT Fl_RGB_Image : public Fl_Image {
 public:
 
   /** Points to the start of the object's data array
+   \see class Fl_SVG_Image which delays initialization of this member variable.
    */
   const uchar *array;
   /** If non-zero, the object's data array is delete[]'d when deleting the object.
@@ -332,6 +334,12 @@ public:
    \sa  void Fl_RGB_Image::max_size(size_t)
    */
   static size_t max_size() {return max_size_;}
+  /** Returns whether an image is an Fl_SVG_Image or not.
+  This virtual method returns a pointer to the Fl_SVG_Image if this object is an instance of Fl_SVG_Image or NULL if not. */
+  virtual Fl_SVG_Image *as_svg_image() { return NULL; }
+  /** Makes sure the object is fully initialized.
+   In particular, makes sure member variable \ref array is non-null. */
+  virtual void normalize() {}
 };
 
 #endif // !Fl_Image_H

FL/Fl_SVG_Image.H

@@ -31,7 +31,7 @@ struct NSVGimage;
  if the file could not be opened or read, and ERR_FORMAT if the SVG format could not be decoded. 
  If the image has loaded correctly, w(), h(), and d() should return values greater than zero.
 
- Rasterization is not done until the image is first drawn or resize() is called. Therefore, 
+ Rasterization is not done until the image is first drawn or resize() or normalize() is called. Therefore, 
  \ref array is NULL until then. The delayed rasterization ensures an Fl_SVG_Image is always rasterized
  to the exact screen resolution at which it is drawn.
 
@@ -161,6 +161,8 @@ public:
   virtual void color_average(Fl_Color c, float i);
   virtual void draw(int X, int Y, int W, int H, int cx = 0, int cy = 0);
   void draw(int X, int Y) { draw(X, Y, w(), h(), 0, 0); }
+  virtual Fl_SVG_Image *as_svg_image() { return this; };
+  virtual void normalize();
 };
 
 #endif // FL_SVG_IMAGE_H