Fixing #4809
The form has a button with a disabled condition, unfortunately there was
an error in checking the condition.
```
disabled={
SignInUpStep.Init
? false
...
```
SignInUpStep.Init is always equal to true, so the first arm was
returning false and button was never disabled. Fixing this check fixes
the double mouse click bug as expected.
```
disabled={
signInUpStep === SignInUpStep.Init
```
Still, the enter keypress is handled a little bit differently. There is
a handleKeyDown event that was ignoring if the form is submitting or
not. I added the check for that, and now pressing enter multiple times
does not result in any errors
ffda4058e0