http2: detect prematures close without data transfered

... by using the regular Curl_http_done() method which checks for
that. This makes test 1801 fail consistently with error 56 (which seems
fine) to that test is also updated here.

Reported-by: Ben Darnell
Bug: https://github.com/bagder/curl/issues/166

lib/http2.c

@@ -102,7 +102,7 @@ const struct Curl_handler Curl_handler_http2 = {
   "HTTP2",                              /* scheme */
   ZERO_NULL,                            /* setup_connection */
   Curl_http,                            /* do_it */
-  ZERO_NULL,                            /* done */
+  Curl_http_done,                       /* done */
   ZERO_NULL,                            /* do_more */
   ZERO_NULL,                            /* connect_it */
   ZERO_NULL,                            /* connecting */
@@ -122,7 +122,7 @@ const struct Curl_handler Curl_handler_http2_ssl = {
   "HTTP2",                              /* scheme */
   ZERO_NULL,                            /* setup_connection */
   Curl_http,                            /* do_it */
-  ZERO_NULL,                            /* done */
+  Curl_http_done,                       /* done */
   ZERO_NULL,                            /* do_more */
   ZERO_NULL,                            /* connect_it */
   ZERO_NULL,                            /* connecting */

tests/data/test1801

@@ -62,5 +62,9 @@ Upgrade: %H2CVER
 HTTP2-Settings: AAMAAABkAAQAAP__
 
 </protocol>
+# nothing is returned, because no HTTP/2 data nor headers was handled
+<errorcode>
+56
+</errorcode>
 </verify>
 </testcase>