fix #1408, HSQLDBDelegate cannot read H2 file blobs

[dcheng1248]

This PR allows Blobs stored in H2 file format to be read by the HSQLDBDelegate.

Fixes issue #1408

Changes

• Checks whether a Blob is a LobInputStream before calling available(), as LobInputStream has available() return 0 even if there is content.

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Checklist

• tested locally
• updated the docs: N/A
• added appropriate test: work in progress, but was suggested to create PR for code change first
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https://github.com/quartz-scheduler/contributing/blob/main/CONTRIBUTING.md