main: avoid a NULL dereference on initialisation.

Reviewed-by: NTim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/10495)

apps/openssl.c

@@ -276,6 +276,13 @@ int main(int argc, char *argv[])
     }
 
     prog = prog_init();
+    if (prog == NULL) {
+        BIO_printf(bio_err,
+                   "FATAL: Startup failure (dev note: prog_init() failed)\n");
+        ERR_print_errors(bio_err);
+        ret = 1;
+        goto end;
+    }
     pname = opt_progname(argv[0]);
 
     /* first check the program name */