clang: Workaround for empty problem ranges at start of document

Sometimes, for some reason we seem to get problem ranges from libclang that
start and end on the first character of the document. As a result, the final
range computed for the ClangProblem will wrongly start from the beginning of the
document and extend until the actual location of the problem. This commit
introduces a workaround which discards the problematic problem ranges.
1 job for !64 with clang_discard_empty_problem_ranges_at_document_start in 46 minutes and 49 seconds (queued for 2 seconds)
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linux kf5-qt5 qt5.12

00:46:49

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