Fix: crash when examining discoveries with '`' in certain cases

The curses version of yn_function could return whitespace characters if the default was '\0'. This leads to a crash if you use the '`' option with curses enabled and a traditional/combination menu style (see doclassdisco() in o_init.c). Allow '\0' to be returned as a default. The tty version allows this, so it should not lead to unexpected input for other yn_function calls (I tested several to be sure).

Author: saltwaterterrapin

doc/evilhack-changelog.md

@@ -3340,3 +3340,4 @@ The following changes to date are:
 - Fix: fixedness knowledge preventing merging of supermaterials
 - Fix: a couple cases of bracers preventing wielding bimanual weapons
 - Restore auto-suppression of some dangerous attacks
+- Fix: crash when examining discoveries with '`' in certain cases

win/curses/cursdial.c

@@ -318,7 +318,7 @@ curses_character_input_dialog(const char *prompt, const char *choices,
             }
             break;
         } else if ((answer == '\n') || (answer == '\r') || (answer == ' ')) {
-            if ((choices != NULL) && (def != '\0')) {
+            if (choices != NULL) {
                 answer = def;
             }
             break;