fix: Ensure sourcemap `sourcesContent` exists before trying to consume

[rschristian]

Closes #926

Per the spec, sourcesContent is optional so we need to check for its existence before consuming.

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🦋 Changeset detected

Latest commit: 2c251f0ceeaaa802c73efb628122c93b21976565

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

| Name | Type | | ---- | ----- | | wmr | Patch |

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Size Change: 0 B

Total Size: 805 kB

ℹ️ View Unchanged

| Filename | Size | | :--- | :---: | | `examples/demo/dist/about/index.html` | 720 B | | `examples/demo/dist/alias-outside/index.html` | 697 B | | `examples/demo/dist/assets/Calendar.********.css` | 694 B | | `examples/demo/dist/assets/style.********.css` | 624 B | | `examples/demo/dist/chunks/alias-outside.********.js` | 139 B | | `examples/demo/dist/chunks/class-fields.********.js` | 211 B | | `examples/demo/dist/chunks/compat.********.js` | 16.9 kB | | `examples/demo/dist/chunks/hoofd.module.********.js` | 1.48 kB | | `examples/demo/dist/chunks/index.********.js` | 303 B | | `examples/demo/dist/chunks/json.********.js` | 238 B | | `examples/demo/dist/chunks/meta-tags.********.js` | 298 B | | `examples/demo/dist/chunks/prerender.********.js` | 294 B | | `examples/demo/dist/class-fields/index.html` | 709 B | | `examples/demo/dist/compat/index.html` | 1.56 kB | | `examples/demo/dist/env/index.html` | 786 B | | `examples/demo/dist/error/index.html` | 714 B | | `examples/demo/dist/files/index.html` | 743 B | | `examples/demo/dist/index.********.js` | 8.2 kB | | `examples/demo/dist/index.html` | 775 B | | `examples/demo/dist/json/index.html` | 720 B | | `examples/demo/dist/lazy-and-late/index.html` | 723 B | | `examples/demo/dist/meta-tags/index.html` | 789 B | | `packages/wmr/wmr.cjs` | 767 kB |

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