Another memory simplification.

dw/findtext.hh

@@ -7,6 +7,9 @@
 
 #include <ctype.h>
 
+#include <optional>
+#include <string>
+
 namespace dw {
 namespace core {
 
@@ -34,7 +37,7 @@ private:
     * If dw::core::Findtext::search is called with the same key, the search
     * is continued, otherwise it is restarted.
     */
-   char *key;
+   std::optional< std::string > key;
 
    /** \brief Whether the last search was case sensitive. */
    bool caseSens;