Fix a pathological case for 2d EB (#2840)

What could happen is a cell might be cut a tiny bit at a corner such that 3
faces with an area fraction of one and one face with an area fraction of
almost one, and the volume fraction is one.  In that case, the boundary area
and centroid have been set to wrong values based on an incorrect assumption.

Src/EB/AMReX_EB2_2D_C.cpp

@@ -31,30 +31,21 @@ void set_eb_data (const int i, const int j,
     const Real nxabs = amrex::Math::abs(nx);
     const Real nyabs = amrex::Math::abs(ny);
 
-    Real x_ym;
-    Real x_yp;
-    Real signx;
-    Real y_xm;
-    Real y_xp;
-    Real signy;
+    Real x_ym, x_yp, y_xm, y_xp;
     if (nx > 0.0_rt) {
         x_ym = -0.5_rt + aym;
         x_yp = -0.5_rt + ayp;
-        signx = 1.0_rt;
     } else {
         x_ym = 0.5_rt - aym;
         x_yp = 0.5_rt - ayp;
-        signx = -1.0_rt;
     }
 
     if (ny > 0.0_rt) {
         y_xm = -0.5_rt + axm;
         y_xp = -0.5_rt + axp;
-        signy = 1.0_rt;
     } else {
         y_xm = 0.5_rt - axm;
         y_xp = 0.5_rt - axp;
-        signy = -1.0_rt;
     }
 
     barea(i,j,0) = nx*(axm-axp) + ny*(aym-ayp);
@@ -64,20 +55,20 @@ void set_eb_data (const int i, const int j,
     bnorm(i,j,0,1) = ny;
 
     if (nxabs < tiny || nyabs > almostone) {
-        barea(i,j,0) = 1.0_rt;
-        bcent(i,j,0,0) = 0.0_rt;
-        bnorm(i,j,0,0) = 0.0_rt;
-        bnorm(i,j,0,1) = signy;
         vfrac(i,j,0) = 0.5_rt*(axm+axp);
         vcent(i,j,0,0) = 0.0_rt;
-        vcent(i,j,0,1) = (0.125_rt*(ayp-aym) + ny*0.5_rt*bcent(i,j,0,1)*bcent(i,j,0,1)) / (vfrac(i,j,0) + 1.e-30_rt);
+        if (vfrac(i,j,0) > almostone) {
+            vcent(i,j,0,1) = 0.0_rt;
+        } else {
+            vcent(i,j,0,1) = (0.125_rt*(ayp-aym) + ny*0.5_rt*bcent(i,j,0,1)*bcent(i,j,0,1)) / (vfrac(i,j,0) + 1.e-30_rt);
+        }
     } else if (nyabs < tiny || nxabs > almostone) {
-        barea(i,j,0) = 1.0_rt;
-        bcent(i,j,0,1) = 0.0_rt;
-        bnorm(i,j,0,0) = signx;
-        bnorm(i,j,0,1) = 0.0_rt;
         vfrac(i,j,0) = 0.5_rt*(aym+ayp);
-        vcent(i,j,0,0) = (0.125_rt*(axp-axm) + nx*0.5_rt*bcent(i,j,0,0)*bcent(i,j,0,0)) / (vfrac(i,j,0) + 1.e-30_rt);
+        if (vfrac(i,j,0) > almostone) {
+            vcent(i,j,0,0) = 0.0_rt;
+        } else {
+            vcent(i,j,0,0) = (0.125_rt*(axp-axm) + nx*0.5_rt*bcent(i,j,0,0)*bcent(i,j,0,0)) / (vfrac(i,j,0) + 1.e-30_rt);
+        }
         vcent(i,j,0,1) = 0.0_rt;
     } else {
         Real aa = nxabs/ny;