[sebxt]

The random access implementation of search_n did not count the mismatching element after a forward scan, so tailSize was one too large. That let the outer loop step lookAhead onto last, which reads out of bounds and can return a match that extends past the end of the range.

Example: search_n(a, a + 4, 2, 1) with a = { 0, 1, 0, 1, 1 } returned a + 3 instead of a + 4.

Changes:

• Subtract the mismatching element from tailSize as well.
• Add regression cases to TestAlgorithm.cpp. Each array has trailing elements outside the searched range so the old behavior is caught without a sanitizer.

The new checks fail before the change and pass after it. The full EASTLTest suite passes (Debug, clang, macOS x86_64).

Fixes #599