Add missing initialisation in DENORM copy constructor

This fixes a Coverity Scan issue:

    1487976 Uninitialized pointer read

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

src/ccstruct/normalis.cpp

@@ -42,6 +42,8 @@ DENORM::DENORM() {
 
 DENORM::DENORM(const DENORM &src) {
   rotation_ = nullptr;
+  x_map_ = nullptr;
+  y_map_ = nullptr;
   *this = src;
 }