free NULL cleanup

This commit handles BIO_ACCEPT_free BIO_CB_FREE BIO_CONNECT_free
BIO_free BIO_free_all BIO_vfree

Reviewed-by: Matt Caswell <matt@openssl.org>
diff --git a/apps/dsa.c b/apps/dsa.c
index 8d085bc..1ea0d73 100644
--- a/apps/dsa.c
+++ b/apps/dsa.c
@@ -356,10 +356,8 @@
     } else
         ret = 0;
  end:
-    if (in != NULL)
-        BIO_free(in);
-    if (out != NULL)
-        BIO_free_all(out);
+    BIO_free(in);
+    BIO_free_all(out);
     DSA_free(dsa);
     if (passin)
         OPENSSL_free(passin);