fix(streaming): handle boundary-not-found in multipart stream transformers

[ankit25bcs10610]

What

In getFormdataToFormdataStreamTransformer and formDataToOctetStreamTransformer:

const boundaryIndex = buffer.indexOf(boundary);
const safeLength = boundaryIndex ?? buffer.length;
const content = buffer.slice(0, safeLength);

String.prototype.indexOf returns -1 when the boundary isn't found. -1 is not nullish, so ?? buffer.length never triggers and safeLength becomes -1.

When a file chunk arrives before its closing boundary — the normal case for large uploads streamed across multiple reads — this means:

• buffer.slice(0, -1) emits the content minus its last byte, and
• the non-file branch does buffer = buffer.slice(-1), discarding almost the entire buffer.

The result is corrupted chunked file uploads.

Fix

Only fall back to buffer.length when the boundary is genuinely absent:

const safeLength = boundaryIndex === -1 ? buffer.length : boundaryIndex;

Applied at both sites. npm run format:check passes.

Note: these transformers operate on a ReadableStream/TransformStream pipeline, so I did not add a unit test (would require standing up the full stream harness). Happy to add one if you'd prefer — the change itself is a self-contained correctness fix.