fix(view): treat a view name ending in "." as extensionless

[bilashcse]

Closes #7350

Problem

path.extname('index.') returns '.', which is truthy but is not a usable extension. View assigned this.ext = extname(name) directly, so for a view name ending in a dot the if (!this.ext) default-engine fallback was skipped, this.ext.slice(1) evaluated to an empty string, and the engine loader called require(''). That throws TypeError [ERR_INVALID_ARG_VALUE] synchronously out of app.render() / res.render() instead of surfacing the usual lookup error through the callback.

Fix

Treat a lone '.' returned by path.extname() as "no extension", so a name with a trailing dot follows the same code path as any other extensionless name. With view engine set, the default engine is appended and lookup fails normally, producing Failed to lookup view "user.". Without view engine set, the existing No default engine was specified and no extension was provided. error is raised. An inline comment above the change documents the edge case.

Tests

test/app.render.js asserts that app.render('user.', cb) no longer throws and that the callback receives a lookup error. test/res.render.js asserts that res.render('user.') responds 500 with Failed to lookup view "user." when view engine is set, and 500 with No default engine was specified when it is not.

Notes

Behaviour is unchanged for any name that does not end in a dot, because path.extname() only returns '.' in that case.

[krzysdz]

Duplicate of #7351