fix(csv): return empty array for empty input with skipFirstRow

[murataslan1]

Description

Fixes #6809

When parsing an empty string with skipFirstRow: true, the function was throwing a TypeError because there were no headers to extract. This is inconsistent with parsing an empty string without options, which returns an empty array.

Problem

parse('');                          // [] ✓
parse(' ', { skipFirstRow: true }); // [] ✓
parse('', { skipFirstRow: true });  // TypeError: Cannot parse input: headers must be defined ✗

Solution

Return an empty array when there's no data to parse, instead of throwing an error.

Changes

if (options.skipFirstRow) {
  const head = r.shift();
  if (head === undefined) {
-   throw new TypeError("Cannot parse input: headers must be defined");
+   return [] as ParseResult<ParseOptions, T>;
  }
  headers = head;
}

After

parse('');                          // [] ✓
parse('', { skipFirstRow: true });  // [] ✓

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