message: Fix the output DType of IsZero() function
diff: @@ -81,7 +81,7 @@ FunctionDef IsZero() {
  // Args
  {"x: T"},
  // Return values
  - {"equal: T"},
  + {"equal: bool"},
  // Attr def
  {"T:{float, double, int32, int64, string}"},
  {
  