secur32: Fill a SECBUFFER_MISSING buffer if the message is not complete.

dlls/secur32/schannel.c

@@ -1244,6 +1244,15 @@ static SECURITY_STATUS SEC_ENTRY schan_DecryptMessage(PCtxtHandle context_handle
     if(buffer->cbBuffer < expected_size)
     {
         TRACE("Expected %u bytes, but buffer only contains %u bytes\n", expected_size, buffer->cbBuffer);
+        buffer->BufferType = SECBUFFER_MISSING;
+        buffer->cbBuffer = expected_size - buffer->cbBuffer;
+
+        /* This is a bit weird, but windows does it too */
+        idx = schan_find_sec_buffer_idx(message, 0, SECBUFFER_EMPTY);
+        buffer = &message->pBuffers[idx];
+        buffer->BufferType = SECBUFFER_MISSING;
+        buffer->cbBuffer = expected_size - buffer->cbBuffer;
+
         TRACE("Returning SEC_E_INCOMPLETE_MESSAGE\n");
         return SEC_E_INCOMPLETE_MESSAGE;
     }