Optimize Jekyll::Filters#item_property

[ashmaroli]

• This is a 🐛 bug fix.

Summary

• property.split(".").reduce(liquid_data) only if property is a dot-notation string.
  Otherwise, property need not be split into a single-element array just to be reduced with the liquid_data object.
• liquid_data.respond_to?(:[]) && liquid_data[key].
  Since a first-pass to :reduce can result in nil, a subsequent pass should be guarded.
  e.g. when property == "author.name" and page.author == nil
• Minor refactoring:
  • property = property.to_s instead of multiple property.to_s
  • call #parse_sort_input at the end of method instead of placing a call at end of each conditional branch

Context

Resolves #6939
Closes #6992

[ashmaroli]

Profiler Summary

--- master branch https://travis-ci.org/jekyll/jekyll/jobs/567626937
+++ PR branch     https://travis-ci.org/jekyll/jekyll/jobs/571688230

- Total allocated: 485.18 MB (4549242 objects)
- Total retained:  19.16 MB (100616 objects)
+ Total allocated: 481.26 MB (4489114 objects)
+ Total retained:  19.17 MB (100692 objects)

[mattr-]

Looks good if we can get the test suites to pass. 😅

[DirtyF]

All green 🍏

@jekyllbot: merge +fix