add missing if condition on write_tb

[qiaojunfeng]

It seems the if condition on write_tb is missing. If setting write_tb = true in win file, the code doesn't write seedname_tb.dat file.

[codecov]

Codecov Report

Merging #309 into develop will decrease coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop     #309      +/-   ##
===========================================
- Coverage    65.60%   65.57%   -0.04%     
===========================================
  Files           29       29              
  Lines        17938    17910      -28     
===========================================
- Hits         11768    11744      -24     
+ Misses        6170     6166       -4     

Impacted Files	Coverage Δ
src/io.F90	58.08% <0.00%> (-2.39%)	⬇️
test-suite/library-mode-test/test_library.F90	64.70% <0.00%> (-0.35%)	⬇️
src/postw90/postw90.F90	86.74% <0.00%> (-0.16%)	⬇️
src/comms.F90	52.63% <0.00%> (-0.16%)	⬇️
src/wannier_prog.F90	81.81% <0.00%> (-0.15%)	⬇️
src/parameters.F90	82.79% <0.00%> (-0.06%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 353cb8e...7b3a217. Read the comment docs.