GenerateOneTimeTokenFilter should not attempt to generate a token with a null token request

[jzheaux]

Related to #16291

GenerateOneTimeTokenFilter attempts to generate a token, even when the token generation request is null:

		GenerateOneTimeTokenRequest generateRequest = this.requestResolver.resolve(request);
		OneTimeToken ott = this.tokenService.generate(generateRequest);
		if (generateRequest == null) {
			filterChain.doFilter(request, response);
			return;
		}

Given that the filter becomes a no-op if generateRequest is null, then it's clearer and less work if tokenService.generate is invoked after the if statement.