Error running workflows with updatehash=True

[mauriliogenovese]

Any workflow running with updatehash=True will crash

That happens because in nodes.py line 457 we try to update the hashfile even if the node was never executed before, so no hashfile is found and _update_hash function raises an exception.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.04%. Comparing base (bc456dd) to head (88e30f8).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3709   +/-   ##
=======================================
  Coverage   73.04%   73.04%           
=======================================
  Files        1278     1278           
  Lines       59356    59357    +1     
=======================================
+ Hits        43359    43360    +1     
  Misses      15997    15997           

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[effigies]

Lgtm. Small logic simplification.

[mauriliogenovese]

I add another commit to keep multi process functionality with updatehash=True.
Maybe there is a more elegant way to address it, but it seems to work in my tests