Fix compile error

src/civetweb.c

@@ -14369,7 +14369,7 @@ ssl_servername_callback(SSL *ssl, int *ad, void *arg)
 	 * Multiple HTTPS hosts on one IP+port are only possible
 	 * with a certificate containing all alternative names.
 	 */
-    if ((servername == NULL) || (*servername = 0)) {
+    if ((servername == NULL) || (*servername == 0)) {
 		DEBUG_TRACE("%s", "SSL connection not supporting SNI");
 		return SSL_TLSEXT_ERR_NOACK;
 	}