Table interpolation for default values improved.

If there were no non-defaulted elements in the table, we would crash.
Now, all defaulted elements get the value 0.0 instead.

The usage pattern was encountered for the capillary pressure column
of a SWOF table.

opm/core/eclipse/EclipseGridParserHelpers.hpp

@@ -398,10 +398,17 @@ namespace
 			yv.push_back(table[k][i]);		    
 		    }
 		}
-		// Interpolate
-		for (int i=0; i<int(indx.size()); ++i) {
-		    table[k][indx[i]] = linearInterpolationExtrap(xv, yv, x[i]);
-		}
+                if (xv.empty()) {
+                    // Nothing specified, insert zeros.
+                    for (int i=0; i<int(indx.size()); ++i) {
+                        table[k][indx[i]] = 0.0;
+                    }
+                } else {
+                    // Interpolate
+                    for (int i=0; i<int(indx.size()); ++i) {
+                        table[k][indx[i]] = linearInterpolationExtrap(xv, yv, x[i]);
+                    }
+                }
 	    }
 	}
     }