distributed roots problem with redistributePar

highlighted on EP1928 - regression when running with distributed roots

assigned to @mark

• problem seems to be related to remnant parallel communication within fvMeshSubset(mesh, zero{}) where it is trying to read fvSchemes/fvSolution.

• patched up by disabling parRun for these calls, but the more proper fix may come with the next release after @Mattijs does some more magic with file handlers, and we may add in lazier evaluation for fvSchemes etc.

mentioned in commit 7b94573a

• premature analysis. Problem is not the parallel communication per se, but that the READ_IF_PRESENT shouldn't be used at all for a (zero-sized) subset. Should be copying in the schemes/solution setting from the parent base-mesh.

mentioned in issue #2524

mentioned in commit 39d89648

closed

I confirm that the bug is resolved.