x509v3/v3_purp.c: resolve Thread Sanitizer nit.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from openssl#6891)

(cherry picked from commit 0da7358)

Author: Andy Polyakov

crypto/x509v3/v3_purp.c

@@ -350,12 +350,8 @@ static void x509v3_cache_extensions(X509 *x)
     ASN1_BIT_STRING *ns;
     EXTENDED_KEY_USAGE *extusage;
     X509_EXTENSION *ex;
-
     int i;
 
-    if (x->ex_flags & EXFLAG_SET)
-        return;
-
     CRYPTO_THREAD_write_lock(x->lock);
     if (x->ex_flags & EXFLAG_SET) {
         CRYPTO_THREAD_unlock(x->lock);