http2: fix double free due to handling of rst_stream with cancel code
The PR changes add the stream to the pending list on receiving
RST_STREAM
frame with error code nghttp2_cancel
. This is to
avoid the force purging of data on receiving the rst_stream frame.
On force purging, the nghttp2
raises close callback for already
destroyed stream which is causing the double-free memory error.
Fixes: #38964