minor #4046 Token - Added fast isset() path to token->equals() (staabm)

This PR was merged into the 2.12 branch.

Discussion
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Token - Added fast isset() path to token->equals()

looking up the existance of a property via isset() is waaaaay faster then array_key_exists().
we still need array_key_exists() as a fallback, when properties exist with a null-value to work properly. this case is very rare, therefore this can be considered a speedup.

this change speeds up php-cs-fixer by 5.6%.

![image](https://user-images.githubusercontent.com/120441/46920181-bd4c6f00-cfea-11e8-8145-069ff58f63c4.png)

Commits
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577a46a Added fast isset() path to token->equals()

src/Tokenizer/Token.php

@@ -180,11 +180,11 @@ public function equals($other, $caseSensitive = true)
             return $this->content === $otherPrototype;
         }
 
-        if (array_key_exists(0, $otherPrototype) && $this->id !== $otherPrototype[0]) {
+        if ($this->id !== $otherPrototype[0]) {
             return false;
         }
 
-        if (array_key_exists(1, $otherPrototype)) {
+        if (isset($otherPrototype[1])) {
             if ($caseSensitive) {
                 if ($this->content !== $otherPrototype[1]) {
                     return false;