Improve docu of member variable Fl_SVG_Image::proportional - cont'd (#1361)

FL/Fl_SVG_Image.H

@@ -31,10 +31,12 @@ 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.
 
+ Member \ref proportional of an Fl_SVG_Image object must be set to \c false to allow the image
+ object to be rasterized with an altered aspect ratio.
+
  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. Member \ref proportional of an Fl_SVG_Image object
- must be set to \c false to allow this image to be rasterized with an altered aspect ratio.
+ to the exact screen resolution at which it is drawn.
 
  The Fl_SVG_Image class draws images computed by \c nanosvg with the following known limitations
 

src/Fl_Image.cxx

@@ -274,6 +274,8 @@ Fl_RGB_Scaling Fl_Image::RGB_scaling() {
  data_w() and data_h(), respectively
  \note This function generally changes the values returned by the w() and h() member functions.
  In contrast, the values returned by data_w() and data_h() remain unchanged.
+ \note If the processed image is an Fl_SVG_Image, setting \ref Fl_SVG_Image::proportional
+ to \c false is required if \p proportional here is null.
  \version 1.4 (1.3.4 and FL_ABI_VERSION for Fl_Shared_Image only)
 
  Example code: scale an image to fit in a box