Fix 'CVE-2017-1000257'

Merge: curl/curl@13c9a9ded3

r5dev/thirdparty/curl/imap.c

@@ -1141,6 +1141,12 @@ static CURLcode imap_state_fetch_resp(struct connectdata *conn, int imapcode,
         /* The conversion from curl_off_t to size_t is always fine here */
         chunk = (size_t)size;
 
+      if (!chunk) {
+          /* no size, we're done with the data */
+          state(conn, IMAP_STOP);
+          return CURLE_OK;
+      }
+
       result = Curl_client_write(conn, CLIENTWRITE_BODY, pp->cache, chunk);
       if(result)
         return result;