ENH: finiteArea: improve robustness in code sections vulnerable to math errors

It has been observed that the finite-area framework is prone to numerical
issues when zero-valued edge lenghts, edge/face normals and face areas exist.

To improve exception handling at identified code sections to gracefully
overcome math errors, the problematic entities are lower-bounded by SMALL.

applications/solvers/finiteArea/liquidFilmFoam/capillaryCourantNo.H

@@ -4,7 +4,7 @@
         sqrt
         (
             2*M_PI*sigma*sqr(aMesh.edgeInterpolation::deltaCoeffs())
-            *aMesh.edgeInterpolation::deltaCoeffs()
+            *mag(aMesh.edgeInterpolation::deltaCoeffs())
             /rhol
         )
     ).value()*runTime.deltaT().value();