ccstruct/polyblk: Fix memory leak

Coverity report:

CID 1164730 (#1 of 1): Resource leak (RESOURCE_LEAK)
4. leaked_storage: Variable lines going out of scope leaks the storage it points to.

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

ccstruct/polyblk.cpp

@@ -294,6 +294,8 @@ void POLY_BLOCK::fill(ScrollView* window, ScrollView::Color colour) {
       }
     }
   }
+
+  delete lines;
 }
 #endif