ROW: 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 ROW.
    It is good practice to match a copy assignment operator
    with a copy constructor.

Signed-off-by: Stefan Weil <[email protected]>

src/ccstruct/ocrrow.h

@@ -144,6 +144,9 @@ class ROW:public ELIST_LINK
     ROW& operator= (const ROW & source);
 
   private:
+    // Copy constructor (currently unused, therefore private).
+    ROW(const ROW& source);
+
     int32_t kerning;               //inter char gap
     int32_t spacing;               //inter word gap
     TBOX bound_box;              //bounding box