Fix: Emoji categories with subfolders, but no emoji, erroneously duplicate the subfolder's emoji

What does this MR do?

This patch fixes a bug where the category sections in MkEmojiPicker that don't directly have any emoticons, but contain subcategories that do, erroneously duplicate their first child's contents due to a bug in parseAndMergeCategories().

Example:

This only occurs when the parent category is not at the top level - you need to nest categories beyond 2 levels (e.g. "Mutant Standard/smileys/cats" will be duplicated into "Mutant Standard/smileys" if no emoticons are categorised as "Mutant Standard/smileys" directly) for this bug to occur.

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