FIX: Fix TDB line length bugs

[bocklund]

This fixes two bugs related to writing TDB files and reflowing lines:

1. Fixes a bug in reflow_text where lines that are too long and contain no valid linebreak characters would result in an infinite loop of finding the same linebreak_idx and emitting the same line until running out of memory. Now lines that cannot be reflowed to under the linewidth raises an error.
2. Adds a whitespace to the delimiter between species in the CONSTITUENTS line (it's now , instead of ,) so reflow_text can reflow the line at any element. This fixes a bug where phases with many constituents would trigger the infinite loop (and now error) from (1).

A test is added for each case.

[codecov]

Codecov Report

Merging #392 (35acada) into develop (631c41c) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop     #392      +/-   ##
===========================================
+ Coverage    89.95%   89.98%   +0.03%     
===========================================
  Files           44       44              
  Lines         4369     4383      +14     
===========================================
+ Hits          3930     3944      +14     
  Misses         439      439              

Impacted Files	Coverage Δ
pycalphad/io/tdb.py	87.66% <100.00%> (+0.02%)	⬆️
pycalphad/tests/test_database.py	100.00% <100.00%> (ø)

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