KNOWN_BUGS: restore text regarding #2101.

This was added earlier but appears to have been removed accidentally.

AFAICT this is very much still an issue.

-----

I say "accidentally" because the text seems to have harmlessly snuck
into [1] (which makes no mention of it).  [1] was later reverted for
unspecified reasons in [2], presumably because the mentioned issue was
fixed or invalid.

[1] de9fac00c4
[2] 16d1f36940

Closes #2618

docs/KNOWN_BUGS

@@ -115,6 +115,9 @@ problems may have been fixed or changed somewhat since this was written!
  Disabling HTTP Pipelining when there are ongoing transfers can lead to
  heap corruption and crash. https://curl.haxx.se/bug/view.cgi?id=1411
 
+ Similarly, removing a handle when pipelining corrupts data:
+ https://github.com/curl/curl/issues/2101
+
 1.3 STARTTRANSFER time is wrong for HTTP POSTs
 
  Wrong STARTTRANSFER timer accounting for POST requests Timer works fine with