Don't validate a rule server side if it has custom (frontend only) conditions (#183)

Author: kjac

Source/Solution/FormEditor/Validation/Validation.cs

@@ -32,8 +32,12 @@ public bool IsValidFor(IEnumerable<FieldWithValue> allCollectedFieldValues, IPub
 				}
 			}
 
-			// the validation fails if all rules are fulfilled
-			Invalid = Rules.Where(r => r.IsApplicable).All(r => r.IsFulfilledBy(allCollectedFieldValues, content));
+			Invalid = Rules.Any(r => r.IsApplicable == false)
+				// it's impossible to validate the rule if we have frontend only conditions in play
+				? false
+				// the validation fails if all rules are fulfilled
+				: Rules.All(r => r.IsFulfilledBy(allCollectedFieldValues, content));
+
 			return Invalid == false;
 		}
 	}