apps/cmp.c: fix crash with -batch option on OPENSSL_NO_UI_CONSOLE

Also make clear we cannot use get_ui_method() at this point.

Fixes #13494
Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/13497)

apps/cmp.c

@@ -2698,13 +2698,10 @@ int cmp_main(int argc, char **argv)
     ret = 0;
 
     if (opt_batch) {
-        UI_METHOD *ui_fallback_method;
 #ifndef OPENSSL_NO_UI_CONSOLE
-        ui_fallback_method = UI_OpenSSL();
-#else
-        ui_fallback_method = (UI_METHOD *)UI_null();
+        UI_method_set_reader(UI_OpenSSL(), NULL);
+        /* can't change get_ui_method() here as load_key_certs_crls() uses it */
 #endif
-        UI_method_set_reader(ui_fallback_method, NULL);
     }
 
     if (opt_engine != NULL)

apps/include/apps_ui.h

@@ -21,7 +21,7 @@ int password_callback(char *buf, int bufsiz, int verify, PW_CB_DATA *cb_data);
 
 int setup_ui_method(void);
 void destroy_ui_method(void);
-const UI_METHOD *get_ui_method(void);
+UI_METHOD *get_ui_method(void);
 
 extern BIO *bio_err;
 

apps/lib/apps_ui.c

@@ -136,7 +136,7 @@ void destroy_ui_method(void)
     }
 }
 
-const UI_METHOD *get_ui_method(void)
+UI_METHOD *get_ui_method(void)
 {
     return ui_method;
 }