Avoid segfault if error during construction of POINT_PROCESS

[nrnhines]

Includes test that the error is recoverable. Errors happen if there is no section or if the position parameter is out of range.

Closes #1625

[codecov-commenter]

Codecov Report

Merging #1627 (b6f1339) into master (d5f6139) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1627      +/-   ##
==========================================
- Coverage   45.19%   45.16%   -0.04%     
==========================================
  Files         551      551              
  Lines      111183   111184       +1     
==========================================
- Hits        50253    50212      -41     
- Misses      60930    60972      +42     

Impacted Files	Coverage Δ
src/nrnoc/point.cpp	79.61% <100.00%> (+0.09%)	⬆️
src/nrnmpi/bbsmpipack.cpp	82.56% <0.00%> (-10.77%)	⬇️
src/parallel/bbsclimpi.cpp	50.00% <0.00%> (-8.14%)	⬇️
src/parallel/bbssrvmpi.cpp	42.16% <0.00%> (-6.03%)	⬇️
src/parallel/bbs.cpp	74.26% <0.00%> (-1.69%)	⬇️
src/nrnoc/cabcode.cpp	71.52% <0.00%> (+0.08%)	⬆️
src/oc/code2.cpp	52.79% <0.00%> (+0.25%)	⬆️

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