In debug builds, initialize newmenu_item type,text to poison values

This improves the chance that an unset value will abort rather than
displaying strange results.  Release builds are unchanged.

common/main/newmenu.h

@@ -209,13 +209,21 @@ public:
 			? &nm_private.input
 			: nullptr;
 	}
-	char    *text;          // The text associated with this item.
+	char    *text
+#ifndef NDEBUG
+		= reinterpret_cast<char *>(UINTPTR_MAX);
+#endif
+		;          // The text associated with this item.
 	int     value;          // For checkboxes and radio buttons, this is 1 if marked initially, else 0
 	// The rest of these are used internally by by the menu system, so don't set 'em!!
 	short   x, y;
 	short   w, h;
 	uint8_t right_offset;
-	nm_type type;           // What kind of item this is, see NM_TYPE_????? defines
+	nm_type type
+#ifndef NDEBUG
+		= static_cast<nm_type>(UINT8_MAX);
+#endif
+		;           // What kind of item this is, see NM_TYPE_????? defines
 	union nm_type_specific_data {
 		nm_type_specific_data() :
 			input{{nullptr, 0, 0}}