Fix a simple html reader bug

[hunterhector]

This PR fixes #871.

Description of changes

1. move collect_span after all the handling of k value, which makes it larger than 0 (should be larger than i).
2. Also make sure k > i before calling collect_span

Possible influences of this PR.

The output of html_reader is likely to change a bit on wrong tags and some whitespaces.

Test Conducted

1. Added the test case with incomplete tags

[codecov]

Codecov Report

Merging #872 (08498ed) into master (87ed581) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #872   +/-   ##
=======================================
  Coverage   80.75%   80.75%           
=======================================
  Files         254      254           
  Lines       19373    19370    -3     
=======================================
- Hits        15644    15642    -2     
+ Misses       3729     3728    -1     

Impacted Files	Coverage Δ
forte/data/readers/html_reader.py	67.06% <100.00%> (+<0.01%)	⬆️
tests/forte/data/readers/html_reader_test.py	98.76% <100.00%> (ø)

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