Balance chapter HTML and fix intro-material italics leaking into text

[LAfricain]

Follow-up to #921: while chapter intro material (book/section headings) is meant to render in italics via ".introMaterial { font- style: italic; }", two related bugs let that styling — and malformed markup in general — leak into the rest of the chapter on modules with rich introductions (e.g. FreCrampon).

• GTKChapDisp::introMaterial() (src/main/display.cc): SWORD's OSIS filter can emit an opening <div type="subSection" ...> for a section heading with no matching closing anywhere in the fetched text. Now counts

  /
  occurrences and appends any missing closing tags before closing our own wrapper, so the block is always self-balanced regardless of what the filter provides.

• wk_html_sanitize() (src/webkit/wk-html.c): parses the final assembled HTML with libxml2 (HTML_PARSE_RECOVER) and re-serializes it before handing it to WebKit, rather than letting WebKit's own parser silently repair mismatched tags unpredictably. General safety net for similar cases we may not have found yet.

• CSS: added ".introMaterial h2.chapterHeader { font-style: normal; }" so section/chapter titles stay upright — only the narrative intro text should be italic, not its headings.

[karlkleinpaste]

I had thought this change was benign so I merged it easily.

But now, having used it some more, I'm finding 2 serious problems.

• The code generates verse alignment anchors ("chapter * 1000 + verse"), and on navigation, sets top alignment to the current verse's anchor. With this latest update, anchors are not reliably top-aligned. (Sometimes they are. More often they are not.) With whole book rendering enabled, navigate to a sample spot in a large book; here, I used Deu 24:17. This top alignment does not occur at that point -- in my example, it "aligns" to page bottom. This is not specific to any module: NASB and ESV also go to page bottom.

• The placement of pre-verse headings is broken with respect to the text and to the end-of-chapter horizontal separator. See right column.

With change:

ESV, showing mis-aligned horizontal separator and excess whitespace following the next pre-verse heading:

With change reverted in a local branch, showing normal whitespace after pre-verse heading, and proper placement of horizontal separator:

Either I will revert this or an update is needed to restore correct anchor alignment and header + separator placement.

[LAfricain]

Let me work on it. Tomorrow or Monday.