Fixes "wrong" behavior to the correct one as described in the bug report.
Before the fix pressing "10 * / 5 =" normally would result in 20 (Stack: (10,*), (10,/), (5,=)) but with those changes it results in 2 (Stack: (10, /), (5, =)).
Internally this is achieved by "blocking" node adding after a operator (*,-,/,...) has been pressed until a number is entered. If another operator is pressed whilst blocked the top (last) operator is changed instead.
BUG: 57349