Bilinear div-by-zero fix

Probably temporary if this will be replaced with Roman's int version, but
better have it anyway.


git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@10281 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

src/Fl_Image.cxx

@@ -338,7 +338,7 @@ Fl_Image *Fl_RGB_Image::copy(int W, int H) {
                    downright[i] * rightf) * downf;
         }
 
-        if (d() == 4) {
+        if (d() == 4 && new_ptr[3]) {
           for (i = 0; i < 3; i++) {
             new_ptr[i] /= new_ptr[3] / 255.0f;
           }