Ensure generated_html? handles single line files

[lildude]

Description

Whilst testing for the next release of Linguist, I found one of the GitHub.com tests failed as follows:

bundler: failed to load command: bin/github-linguist (bin/github-linguist)
NoMethodError: undefined method `start_with?' for nil:NilClass
  /Users/lildude/github/linguist/lib/linguist/generated.rb:612:in `generated_html?'
  /Users/lildude/github/linguist/lib/linguist/generated.rb:89:in `generated?'
  /Users/lildude/github/linguist/lib/linguist/generated.rb:12:in `generated?'
  /Users/lildude/github/linguist/lib/linguist/blob_helper.rb:357:in `generated?'
  /Users/lildude/github/linguist/lib/linguist/lazy_blob.rb:52:in `generated?'
  /Users/lildude/github/linguist/lib/linguist/blob_helper.rb:380:in `include_in_language_stats?'
  /Users/lildude/github/linguist/lib/linguist/repository.rb:164:in `block in compute_stats'
  /Users/lildude/github/linguist/lib/linguist/repository.rb:149:in `each_delta'
  /Users/lildude/github/linguist/lib/linguist/repository.rb:149:in `compute_stats'
  /Users/lildude/github/linguist/lib/linguist/repository.rb:116:in `cache'
  /Users/lildude/github/linguist/lib/linguist/repository.rb:68:in `languages'
  bin/github-linguist:30:in `<top (required)>'

The test is failing on a very simple .html file that contains:

I'm remote.html, a different file loaded with ajax.

The problem is the generated_html? method makes a few assumptions about the number of lines in the file and doesn't consider there may only be a single line.

This PR corrects that behaviour .

Checklist doesn't apply as I'm fixing a bug and we don't have a section for that 😄.

[pchaigno]

LGTM!

We should have a test for this, but I don't see an easy way to write one.

[lildude]

Yeah, I couldn't find an easy way to test this either.

[Alhadis]

Oops, sorry about that. Chalk that one up to my lack of Ruby experience. 😅

@lildude Is there anything I can do to help with whatever's going on at lildude/fix-gen_html-error...? Or is it unrelated to my earlier PR's changes?

Also, major WTF @ the recent commit logs on your branch:

Author: The rugged tests are fragile <colin@github.com>

/cc @TheRuggedFragileTestFormerlyKnownAsLilDude

[lildude]

@lildude Is there anything I can do to help with whatever's going on at lildude/fix-gen_html-error...? Or is it unrelated to my earlier PR's changes?

Just opened a PR for that - #4628

Also, major WTF @ the recent commit logs on your branch:

Author: The rugged tests are fragile <colin@github.com>

Whoops. Not sure how I did that 😊 . Will rewrite my author info.