Move BN_CTX_start() call so the error case can always call BN_CTX_end().

Signed-off-by: NKurt Roeckx <kurt@roeckx.be>
Reviewed-by: NRich Salz <rsalz@openssl.org>
MR #1231

crypto/dsa/dsa_gen.c

@@ -145,10 +145,11 @@ int dsa_builtin_paramgen(DSA *ret, size_t bits, size_t qbits,
     if ((ctx = BN_CTX_new()) == NULL)
         goto err;
 
+    BN_CTX_start(ctx);
+
     if ((mont = BN_MONT_CTX_new()) == NULL)
         goto err;
 
-    BN_CTX_start(ctx);
     r0 = BN_CTX_get(ctx);
     g = BN_CTX_get(ctx);
     W = BN_CTX_get(ctx);