Fix coverity issues (medium)

This MR fixes several medium-level issues found by Coverity Scan.

While less serious, medium-level issues are sometimes slightly more complex to fix because of code intent, and thus more prone to regressions than high-level issues.

    Issues in SEP were set to ignore.
    Some issues set to ignore based on code intent.
    CID1445705 - unchecked cast in details table.
    CID1445707 - unchecked fread returned bytes in StarComponent.
    CID1445708 - unchecked cast in guider interface.
    CID1445711 - unchecked cast in observing list.
    CID1445714 - unchecked cast in details dialog.
    CID1445719 - unchecked cast in details dialog.
    CID1445721 - uninit var hfr in Analyze capture session.
    CID1445725 - unchecked cast in EkosLive message.
    CID1445726 - dead duplicated code in FITS packer.
    CID1445728 - possible division by zero in Scheduler job time estimation.
    CID1445729 - uninit var in Linear Focus.
    CID1445730 - unchecked cast in EkosLive message.
    CID1445734 - uninit vars in SchedulerJob.
    CID1445742 - unintended sign extension in FITS star filtering.
    CID1445743 - unchecked cast in EkosLive message.
    CID1445748 - uninit vars in Meridian Flip test.
    CID1445753 - stray semicolon in Capture test helper macro.
    CID1445757 - fix if construct (sorry Akarsh).

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