Bug 911055 - [zffos1.1][P3][Dailer]DuT doesn allow to dial a <<pause>>

I'm really bad at regex, but this seems to work and looks cleaner to me:
```
/^(?!,)([0-9#+*,]){0,50}$/
```
My test for it:
```js
var regex = /^(?!,)([0-9#+*,]){0,50}$/; console.log(regex.test('123') + ' ' + regex.test(',123') + ' ' + regex.test('1,23') + ' ' + regex.test('a123'));
```
Outputs:
```
true false true false
```