fix(cosmovisor): retry while upgrade-info.json is still empty

[kriss39]

Description

fileWatcher.CheckUpdate handles the case where upgrade-info.json has been created but not yet written (#21086) by polling up to 10 × 2 ms for the write to land. The loop's exit condition is inverted:

for range 10 {
    time.Sleep(2 * time.Millisecond)
    stat, err = os.Stat(fw.filename)
    ...
    if stat.Size() == 0 {
        break
    }
}

It breaks out as soon as the file is still empty, so the "wait for the write" path is effectively a single 2 ms retry, and a write that lands 3–20 ms later is missed until the next ticker interval. In the common case that only delays the upgrade by one poll interval; on a slow disk / loaded host the daemon can be killed on the next tick anyway, so this mostly matters for the guarantee the retry loop was meant to provide.

Changes

• Flip the condition: keep polling while the file is empty, stop as soon as it has content.
• Regression test TestCheckUpdateWaitsForEmptyFileWrite: starts from an empty file, writes the plan 5 ms later from another goroutine, and asserts CheckUpdate picks it up. Fails on main (Should be true), passes with the fix.
• cosmovisor CHANGELOG entry.

[greptile-apps]

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