Handle null returned from parseFrontMatterTags

[chipschipschips]

Issue #24 describes when installing obsidian-query-language that results in users getting the error

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For me, I saw the following error in the console:

Uncaught (in promise) TypeError: Cannot read properties of null (reading 'concat')
    at ObsidianQueryLanguagePlugin.eval (plugin:obsidian-query-language:27276:37)
    at step (plugin:obsidian-query-language:79:23)
    at Object.eval [as next] (plugin:obsidian-query-language:60:53)
    at eval (plugin:obsidian-query-language:53:71)
    at new Promise (<anonymous>)
    at __awaiter (plugin:obsidian-query-language:49:12)
    at ObsidianQueryLanguagePlugin.parseTags (plugin:obsidian-query-language:27265:16)
    at ObsidianQueryLanguagePlugin.eval (plugin:obsidian-query-language:27242:51)
    at step (plugin:obsidian-query-language:79:23)
    at Object.eval [as next] (plugin:obsidian-query-language:60:53)

Which links back to line 100 of this snippet: https://github.com/jplattel/obsidian-query-language/blob/d6205bdd381598e897ec698c116c196be38b5a1d/src/main.ts#L91-L104

Here on line 100, tags can sometimes be null because parseFrontMatterTags can sometimes return null (see the obsidian-api; I didn't see any obvious reason why it might sometimes do that). So this change just sets it to an empty list when that happens.

(This pull request addresses that root cause, but I don't know if everyone would be experiencing the same root cause.)

[jplattel]

Looks good to me! Thanks for finding this outlier! I'll merge and release a new version :)