Fix memory leak in DSA redo case.

Found by clang scan-build.
Signed-off-by: NKurt Roeckx <kurt@roeckx.be>
Reviewed-by: NRichard Levitte <levitte@openssl.org>

RT: #4184, MR: #1496

crypto/dsa/dsa_ossl.c

@@ -191,9 +191,6 @@ static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
     if (!BN_mod_mul(s, s, kinv, dsa->q, ctx))
         goto err;
 
-    ret = DSA_SIG_new();
-    if (ret == NULL)
-        goto err;
     /*
      * Redo if r or s is zero as required by FIPS 186-3: this is very
      * unlikely.
@@ -205,11 +202,14 @@ static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)
         }
         goto redo;
     }
+    ret = DSA_SIG_new();
+    if (ret == NULL)
+        goto err;
     ret->r = r;
     ret->s = s;
 
  err:
-    if (!ret) {
+    if (ret == NULL) {
         DSAerr(DSA_F_DSA_DO_SIGN, reason);
         BN_free(r);
         BN_free(s);