Multiplication and division by negative numbers is broken

[pchiquet]

Simple expressions such as 1/-1 or 1*-1 can not be evaluated.

• It is a regression since a0f978c
• PR with auto tests here Fix "changeSign" precedence for multiplication and division by negative numbers #76
  On master, the tests failed with Cannot read properties of undefined (reading 'value')
  Full log:

  1) Testing Unit dividing by negative number :
     TypeError: Cannot read properties of undefined (reading 'value')
      at t.w [as postfixEval] (C:\Users\pierr\git\contribs\web\math-expression-evaluator\dist\es\index.js:1:6463)
      at t.eval (C:\Users\pierr\git\contribs\web\math-expression-evaluator\dist\es\index.js:1:10931)
      at Context.<anonymous> (C:\Users\pierr\git\contribs\web\math-expression-evaluator\test\index.js:183:21)
      at callFn (C:\Users\pierr\git\contribs\web\math-expression-evaluator\node_modules\mocha\lib\runnable.js:326:21)
      at Test.Runnable.run (C:\Users\pierr\git\contribs\web\math-expression-evaluator\node_modules\mocha\lib\runnable.js:319:7)
      at Runner.runTest (C:\Users\pierr\git\contribs\web\math-expression-evaluator\node_modules\mocha\lib\runner.js:422:10)
      at C:\Users\pierr\git\contribs\web\math-expression-evaluator\node_modules\mocha\lib\runner.js:528:12
      at next (C:\Users\pierr\git\contribs\web\math-expression-evaluator\node_modules\mocha\lib\runner.js:342:14)
      at C:\Users\pierr\git\contribs\web\math-expression-evaluator\node_modules\mocha\lib\runner.js:352:7
      at next (C:\Users\pierr\git\contribs\web\math-expression-evaluator\node_modules\mocha\lib\runner.js:284:14)
      at Immediate._onImmediate (C:\Users\pierr\git\contribs\web\math-expression-evaluator\node_modules\mocha\lib\runner.js:320:5)
      at processImmediate (node:internal/timers:466:21)