Fix four bugs causing PowerPoint repair dialog & missing bullets (#1432, #1440, #1441, #1442)

[rupivbluegreen]

Change Summary

Fixes four small bugs in src/gen-xml.ts, all of which are reported with reproductions and root-cause analysis in the linked issues. Three produce OOXML schema violations that trigger the PowerPoint repair dialog; one silently drops a bullet style.

Change Type

• Bug fix
• New feature
• Documentation update

Related Issues

• Closes bullet: {type: "bullet"} results in no bullet #1432 — bullet: { type: "bullet" } results in no bullet
• Closes [BUG] Table cell margin produces NaN XML attributes when margin is not a number or array #1440 — table cell margin produces NaN XML attributes for invalid input
• Closes [BUG] Shapes without text produce <p:sp> missing <p:txBody>, triggering repair dialog #1441 — shapes without text produce <p:sp> missing <p:txBody>
• Closes [BUG] Solid color background missing <a:effectLst/> in <p:bgPr>, triggers repair dialog #1442 — solid color background missing <a:effectLst/>

Motivation and Context

Three of these (#1440, #1441, #1442) produce OOXML schema violations that cause PowerPoint to show the "PowerPoint found a problem with content" repair dialog when opening a generated file. The fourth (#1432) makes bullet: { type: 'bullet' } — a documented and TypeScript-typed value (type?: 'bullet' | 'number', default 'bullet') — silently produce no bullet. The fixes are minimal and isolated; all four root causes were already debugged by the original reporters.

Change Description

gen-xml.ts:93 — Issue #1442
Solid color background now includes <a:effectLst/>, matching the image-background branch one line above.

-strSlideXml += `<p:bg><p:bgPr>${genXmlColorSelection(slide.background)}</p:bgPr></p:bg>`
+strSlideXml += `<p:bg><p:bgPr>${genXmlColorSelection(slide.background)}<a:effectLst/></p:bgPr></p:bg>`

gen-xml.ts:320 — Issue #1440
Adds two defensive guards after the existing number-to-array conversion:

• if cellMargin is still not an array (i.e. user passed an object or string), fall back to DEF_CELL_MARGIN_IN
• map any non-finite entries to 0 so inch2Emu(undefined) can no longer yield marL=\"NaN\" etc.

gen-xml.ts:890 — Issue #1432
Merges the outer if (bullet.type) and inner if (type === 'number') checks into a single condition so non-number types fall through to the characterCode / code / default branches and produce a normal bullet character.

gen-xml.ts:1158 — Issue #1441
genXmlTextBody() no longer returns an empty string when a non-tablecell object has no text; it returns a minimal valid <p:txBody> (<a:bodyPr/><a:lstStyle/><a:p><a:endParaRPr lang=\"...\"/></a:p>) so the enclosing <p:sp> satisfies the OOXML schema. The lang defaults to opts.lang || 'en-US', consistent with other endParaRPr emissions in this file.

Verification

Built locally with npm run build and ran a small Node script that exercises each scenario and inspects the resulting XML in the generated .pptx:

```
PASS #1442 solid bg includes <a:effectLst/>
PASS #1441 empty-text shape has <p:txBody>
PASS #1440 bogus table margin produces no NaN attributes
PASS #1432 bullet:{type:"bullet"} renders <a:buChar>
```

Confirmed that the same script fails on `master` (without the fix), and `npx eslint src/gen-xml.ts src/gen-objects.ts` passes clean.

Checklist

• My code follows the style guidelines of this project (tabs, single quotes, no semicolons)
• My changes generate no new eslint warnings (lint clean on modified files)
• I have performed a self-review of my code
• I have commented the non-obvious lines (OOXML reasoning, NaN guard rationale)
• I have included verification that the fixes are effective (see above)
• Only src/*.ts modified — no dist or src/bld changes