Fix(mfsfr2.py): dataset 6b and 6c write routine, remove blank lines

[jlarsen-usgs]

• blank lines were previously written to file in the case of isfropt = 2 or 3 and icalc >= 2
• updated t009_test.py to check for this issue

[codecov]

Codecov Report

Merging #1101 (ec3e6d7) into develop (df843e0) will increase coverage by 2.255%.
The diff coverage is 100.000%.

❗ Current head ec3e6d7 differs from pull request most recent head cbe991b. Consider uploading reports for the commit cbe991b to get more accurate results

@@              Coverage Diff              @@
##           develop     #1101       +/-   ##
=============================================
+ Coverage   71.748%   74.003%   +2.255%     
=============================================
  Files          225       221        -4     
  Lines        51856     49296     -2560     
=============================================
- Hits         37206     36481      -725     
+ Misses       14650     12815     -1835     

Impacted Files	Coverage Δ
flopy/modflow/mfsfr2.py	85.082% <100.000%> (-0.113%)	⬇️
flopy/modflow/mfswi2.py	62.229% <0.000%> (-10.079%)	⬇️
flopy/export/metadata.py	15.833% <0.000%> (-6.475%)	⬇️
flopy/datbase.py	72.093% <0.000%> (-4.378%)	⬇️
flopy/discretization/modeltime.py	85.000% <0.000%> (-3.889%)	⬇️
flopy/modflow/mfswr1.py	20.930% <0.000%> (-3.515%)	⬇️
flopy/modflow/mfpbc.py	14.893% <0.000%> (-3.474%)	⬇️
flopy/modflow/mfsor.py	16.981% <0.000%> (-3.019%)	⬇️
flopy/modflow/mfoc.py	91.699% <0.000%> (-2.986%)	⬇️
flopy/discretization/grid.py	71.229% <0.000%> (-2.761%)	⬇️
... and 170 more