Improves performance on large commented logical lines

[hauntsaninja]

Fixes #509

> rm -rf ~/Library/Caches/black; time python3 -m black --check profiling/dict_big.py 
All done! ✨ 🍰 ✨
1 file would be left unchanged.

real	0m2.984s
user	0m2.916s
sys	0m0.051s
> sed -i '' '/21233/s/$/  # comment/' profiling/dict_big.py 
> git diff | cat
diff --git a/profiling/dict_big.py b/profiling/dict_big.py
index f330ac5..27a862d 100644
--- a/profiling/dict_big.py
+++ b/profiling/dict_big.py
@@ -7996,6 +7996,6 @@ config = some.Structure(
         "21229": "AB890X",
         "21230": "AB890X",
         "21231": "AB890X",
-        "21233": "AB890X",
+        "21233": "AB890X",  # comment
     }
 )
> rm -rf ~/Library/Caches/black; time python3 -m black --check profiling/dict_big.py
All done! ✨ 🍰 ✨
1 file would be left unchanged.

real	1m17.364s
user	1m17.007s
sys	0m0.144s
> git checkout comment-perf-fix
M	profiling/dict_big.py
Switched to branch 'comment-perf-fix'
Your branch is ahead of 'origin/master' by 1 commit.
  (use "git push" to publish your local commits)
> rm -rf ~/Library/Caches/black; time python3 -m black --check profiling/dict_big.py
All done! ✨ 🍰 ✨
1 file would be left unchanged.

real	0m3.030s
user	0m2.958s
sys	0m0.053s

[coveralls]

Pull Request Test Coverage Report for Build 798

• 17 of 18 (94.44%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.01%) to 96.094%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
black.py	17	18	94.44%

Totals
Change from base Build 797:	-0.01%
Covered Lines:	2903
Relevant Lines:	3021

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 798

• 17 of 18 (94.44%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.01%) to 96.094%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
black.py	17	18	94.44%

Totals
Change from base Build 797:	-0.01%
Covered Lines:	2903
Relevant Lines:	3021

---

💛 - Coveralls