HTTP2 WINDOW_UPDATE delta is non-zero check

In current implementation for HTTP2 protocol, there is no check that WINDOW_UPDATE frame received from peer has non-zero deltaWindowSize value.

According to the specification https://tools.ietf.org/html/rfc7540#section-6.9:
'A receiver MUST treat the receipt of a WINDOW_UPDATE frame with an
flow-control window increment of 0 as a stream error (Section 5.4.2)
of type PROTOCOL_ERROR; errors on the connection flow-control window
MUST be treated as a connection error (Section 5.4.1).'