fix  --strict-warnings

Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4717)
diff --git a/test/afalgtest.c b/test/afalgtest.c
index ec25d58..adb2977 100644
--- a/test/afalgtest.c
+++ b/test/afalgtest.c
@@ -62,7 +62,7 @@
                                     "\xb1\x9e\xe0\xdf\x61\xb9\xc2\x55\xeb";
     unsigned char encresult_256[] = "\xa0\x76\x85\xfd\xc1\x65\x71\x9d"
                                     "\xc7\xe9\x13\x6e\xae\x55\x49\xb4\x13";
-    unsigned char *enc_result;
+    unsigned char *enc_result = NULL;
 
     int encl, encf, decl, decf;
     int ret = 0;