properly update formula after first operation

app/src/androidTest/java/com/simplemobiletools/calculator/MainActivityTest.java

@@ -158,7 +158,7 @@ public class MainActivityTest {
         press(R.id.btn_2);
         press(R.id.btn_equals);
         checkResult("2");
-        checkFormula("");
+        checkFormula("0+2");
     }
 
     @Test

app/src/main/kotlin/com/simplemobiletools/calculator/helpers/CalculatorImpl.kt

@@ -98,12 +98,8 @@ class CalculatorImpl(calculator: Calculator, val context: Context) {
     }
 
     private fun calculateResult() {
-        if (!mIsFirstOperation) {
-            updateFormula()
-        }
-
+        updateFormula()
         val operation = OperationFactory.forId(mLastOperation!!, mBaseValue, mSecondValue)
-
         if (operation != null) {
             updateResult(operation.getResult())
         }