Fix a bug and add a check in parameters.f90

[qiaojunfeng]

1. It seems that the berry_task check for morb is wrong in parameters.f90, while in the previous version of wannier90 this was correct.

2. I have added a check for kpoint_path block since I accidentally encountered a segmentation fault when plotting kpath. The situation is that if kpath = true while there is no begin kpoint_path ... end kpoint_path block in the input file, the postw90.x will complain:

    Program received signal SIGSEGV: Segmentation fault - invalid memory reference.
   
    Backtrace for this error:
    #0  0x7f63e4604dff in ???
    #1  0x55cc0cdecdd0 in ???
    #2  0x55cc0cd444af in ???
    #3  0x55cc0cd44871 in ???
    #4  0x7f63e45f1222 in ???
    #5  0x55cc0cd4349d in ???
    #6  0xffffffffffffffff in ???
    [1]    14953 segmentation fault (core dumped)  ../../postw90.x Fe
   

   compiled with gfortran 8.2.1 on Linux.

3. I recently implented a new feature of calculating spin Hall conductivity based on wannier90 (https://journals.aps.org/prb/abstract/10.1103/PhysRevB.98.214402). I would like to share my code with the community. If it could be merged into wannier90, I would like to write the corresponding documentaion and tutorials and create a pull request in the next few weeks!

[codecov]

Codecov Report

Merging #258 into develop will decrease coverage by <.01%.
The diff coverage is 66.66%.

@@             Coverage Diff             @@
##           develop     #258      +/-   ##
===========================================
- Coverage    62.04%   62.04%   -0.01%     
===========================================
  Files           29       29              
  Lines        17132    17134       +2     
===========================================
+ Hits         10630    10631       +1     
- Misses        6502     6503       +1

Impacted Files	Coverage Δ
src/parameters.F90	81.73% <66.66%> (-0.02%)	⬇️

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[jryates]

Thanks for this. Yes - if you could make a pull request for the spin Hall code that would be great. Post an issue if you would like to discuss any of the details.