dselect: Fix memory leak in set_color()

Warned-by: coverity

debian/changelog

@@ -9,6 +9,7 @@ dpkg (1.17.9) UNRELEASED; urgency=low
     packages.
   * Fix short lived memory leaks in «dpkg-split --split».
   * Fix memory leak in unused Keybindings screen in dselect.
+  * Do not leak color string on «dselect --color».
 
   [ Updated scripts translations ]
   * French (Steve Petruzzello). Closes: #746350

dselect/main.cc

@@ -304,6 +304,8 @@ extern "C" {
                        color[screenpart].attr= color[screenpart].attr | aval;
       }
     }
+
+    free(s);
   }
 
 } /* End of extern "C" */