[llvm] [llvm-cov][CoverageView] minor fix/improvement to HTML and text coverage output (PR #80952)

[Alan Phipps via llvm-commits]

evodius96 wrote:

LGTM -- thanks for catching these.  It would be great if you could backport this to the 18.x branch.

https://github.com/llvm/llvm-project/pull/80952