fix(ui): prevent fieldErrorsToast from showing empty errors list (#11643)

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### What?

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Fixes #

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### What?
The error toast shown on field errors was _greatly_ improved recently
with much clearer, more easily consumable messages. This PR adjusts a
minor issue when the format of the error message is such that there are
no subsequent field errors present.

### Why?
To prevent showing an extra `li` when there are no more field errors.

### How?
Previously, the error msg array was being constructed like so:
```ts
const [intro, errorsString] = message.split(':')
const errors = (errorsString || '')
    .split(',')
    .map((error) => error.replaceAll(' > ', ' → ').trim())
    
if (errors.length === 0) {
    return {
      message: intro,
    }
}
...
```

This works fine. However, if the initial message split makes
`errorsString` undefined, as is the case where there are no subsequent
field errors, the `(errorsString || '').split(',')` will always return
an array with a single `""` element in it, making the check for
`errors.length === 0` unreachable. This PR checks if `errorsString` is
false-y first before doing further processing instead.

Before:

![Login-Payload-03-11-2025_10_36_PM-before](https://github.com/user-attachments/assets/b2695277-7e33-40c8-a369-de4f72654d5f)

After:

![Login-Payload-03-11-2025_10_35_PM-after](https://github.com/user-attachments/assets/efad92b2-d9c2-4efb-bb67-b1dd625855bf)

Author: akhrarovsaid

packages/ui/src/elements/Toasts/fieldErrors.tsx

@@ -34,16 +34,15 @@ function createErrorsFromMessage(message: string): {
   message: string
 } {
   const [intro, errorsString] = message.split(':')
-  const errors = (errorsString || '')
-    .split(',')
-    .map((error) => error.replaceAll(' > ', ' → ').trim())
 
-  if (errors.length === 0) {
+  if (!errorsString) {
     return {
       message: intro,
     }
   }
 
+  const errors = errorsString.split(',').map((error) => error.replaceAll(' > ', ' → ').trim())
+
   if (errors.length === 1) {
     return {
       errors,