C_OUTLINE_FRAG: Add declaration for copy constructor

It does not need an implementation as it is currently not used.

This fixes a warning from LGTM:

    No matching copy constructor in class C_OUTLINE_FRAG.
    It is good practice to match a copy assignment operator
    with a copy constructor.

Signed-off-by: Stefan Weil <sw@weilnetz.de>

src/textord/fpchop.h

@@ -52,6 +52,8 @@ class C_OUTLINE_FRAG:public ELIST_LINK
     int16_t ycoord;                //coord of cut pt
 
   private:
+    // Copy constructor (currently unused, therefore private).
+    C_OUTLINE_FRAG(const C_OUTLINE_FRAG& other);
 };
 
 ELISTIZEH(C_OUTLINE_FRAG)