curses band-aid

heaputil reported an attempt to free a null pointer at line 1314 of
cursdial.c (in menu_display_page()).

curses_break_str() can return Null but its callers aren't prepared
for that.  Make it return an empty string that can be passed to
free() instead.

win/curses/cursmisc.c

@@ -343,7 +343,12 @@ curses_break_str(const char *str, int width, int line_num)
     }
 
     if (curline < line_num) {
+#if 0
         return NULL;
+#else
+        /* callers aren't prepared to handle NULL return */
+        Strcpy(curstr, "");
+#endif
     }
 
     retstr = curses_copy_of(curstr);