plenumPressureFvPatchScalarField does not initialise all variables in constructor

Summary

plenumPressureFvPatchScalarField sometimes gives sigfpe at startup

Steps to reproduce

Run helmholtzResonance tutorial under valgrind. Shows an uninitialised variable. (workaround is to run with FOAM_SETNAN).

Environment information

• OpenFOAM version : v2406

Possible fixes

Make sure to initialise all in constructors.