html: Add missing condition to 'in cell' insertion mode, required by spec
In section 12.2.6.4.15 of the spec, there is a condition that the current node is a td or th element, which is not implemented. This can lead to a panic when the open elements stack is popped whilst empty, as outlined in golang/go#30600. This commit implements that check.
Fixes golang/go#30600
Change-Id: I4837815e2edce21b58a985a100d93d146bf71e24
GitHub-Last-Rev: 79084c5a8481cd2cf8e4df632ffa358c1e41335b
GitHub-Pull-Request: golang/net#41
Reviewed-on: https://go-review.googlesource.com/c/net/+/172377
Reviewed-by: Kunpei Sakai <namusyaka@gmail.com>
Reviewed-by: Nigel Tao <nigeltao@golang.org>
Run-TryBot: Kunpei Sakai <namusyaka@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>