bug #11169 [Console] Fixed notice in DialogHelper (florianv)

This PR was merged into the 2.3 branch.

Discussion
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[Console] Fixed notice in DialogHelper

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT

When pressing escape in a question, a notice is shown because the sequence is only 2 characters long.

Commits
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ff6c65e [Console] Fixed notice in DialogHelper

src/Symfony/Component/Console/Helper/DialogHelper.php

@@ -150,7 +150,7 @@ class DialogHelper extends Helper
                     $c .= fread($inputStream, 2);
 
                     // A = Up Arrow. B = Down Arrow
-                    if ('A' === $c[2] || 'B' === $c[2]) {
+                    if (isset($c[2]) && ('A' === $c[2] || 'B' === $c[2])) {
                         if ('A' === $c[2] && -1 === $ofs) {
                             $ofs = 0;
                         }