fix(FileResponse): guard 416 response behind range header presence check

[Copilot]

FileResponse was returning 416 Range Not Satisfiable for requests that included no Range header at all — most notably, any request for a 0-byte file, since startFrom defaults to 0 and 0 >= f.length() is true for empty files.

Change

• FileResponse.java line 239: Added range != null && to the satisfiability guard so a 416 is only emitted when the client actually sent a Range header with an out-of-bounds value.

// Before — fires on empty files even without a Range header
if (startFrom < 0 || startFrom >= f.length()) { ... }

// After — only fires when Range was requested and is invalid
if (range != null && (startFrom < 0 || startFrom >= f.length())) { ... }

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