#1888 empty cell getNum error handling

Author: stalgiag

src/io/p5.TableRow.js

@@ -142,6 +142,7 @@ p5.TableRow.prototype.getNum = function(column) {
   }
 
   if (ret.toString() === 'NaN') {
+    console.error('Error: ' + this.obj[column]+ ' is NaN (Not a Number)');
   }
   return ret;
 };