Fix segfault when coverage runs with annotations disabled

[george-bit]

Summary

Sorry about this - the fix I submitted in #2541 didn't fully solve the problem. It turns out there's still a segfault when coverage is running but template annotations are disabled.

What went wrong

When I tested locally, annotations were enabled by default, so everything worked. I didn't realise that in most CI environments (including ours!), annotations are typically disabled. This meant the fix only covered one scenario.

The condition I wrote was too restrictive:

if coverage_running? && ActionView::Base.annotate_rendered_view_with_filenames

This only avoided the negative lineno when both conditions were true. When annotations are disabled (common in CI), it still used lineno = -1, which causes the segfault.

The fix

Always use lineno = 0 when coverage is running, regardless of annotation settings:

if coverage_running?
  @strip_annotation_line = ActionView::Base.annotate_rendered_view_with_filenames
  0
else
  -1
end

The annotation line stripping still only happens when annotations are enabled (since there's nothing to strip otherwise), but we avoid the dangerous negative lineno either way.

Added test

I've added a test specifically for the annotations-disabled case. Unfortunately the segfault only reproduces on Linux, not macOS, so I couldn't verify locally - but it would have caught this if it had been in the original PR.

Again, apologies for not getting this right the first time.

[joelhawksley]

Thanks for the quick fix!