Flush when pop f64

src/calc.rs

@@ -398,6 +398,7 @@ impl Calculator {
         })
     }
     pub fn pop(&mut self) -> CalculatorResult<f64> {
+        self.flush_l()?;
         let f = self.checked_get(0)?;
         self.direct_state_change(CalculatorStateChange {
             pop: OpArgs::Unary(f),