feat: clear result on numpad press when lastKey=EQUALS and lastOperat…

…ion=""

This results in the user being able to type a new calculation
immediately after getting the result of the last calculation instead of
just adding more digits to the end of the result.

app/src/main/kotlin/org/fossify/calculator/helpers/CalculatorImpl.kt

@@ -396,6 +396,9 @@ class CalculatorImpl(
         }
 
         if (lastKey == EQUALS) {
+            if (lastOperation != "") {
+                handleReset()
+            }
             lastOperation = EQUALS
         }