Tokenizers/PHP: bug fix - empty block comment

This commit fixes an edge case tokenizer bug, where a - completely empty, not even whitespace - _block comment_, would be tokenized as a docblock.

Without this commit, the `/**/` code snippet was tokenized as:
```
  8 | L07 | C  1 | CC 0 | ( 0) | T_DOC_COMMENT_OPEN_TAG     | [  4]: /**/
  9 | L07 | C  5 | CC 0 | ( 0) | T_DOC_COMMENT_CLOSE_TAG    | [  0]:
```

With the fix applied, it will be tokenized as:
```
  8 | L07 | C  1 | CC 0 | ( 0) | T_COMMENT                  | [  4]: /**/
```

src/Tokenizers/PHP.php

@@ -786,7 +786,7 @@ protected function tokenize($string)
 
             if ($tokenIsArray === true
                 && ($token[0] === T_DOC_COMMENT
-                || ($token[0] === T_COMMENT && strpos($token[1], '/**') === 0))
+                || ($token[0] === T_COMMENT && strpos($token[1], '/**') === 0 && $token[1] !== '/**/'))
             ) {
                 $commentTokens = $commentTokenizer->tokenizeString($token[1], $this->eolChar, $newStackPtr);
                 foreach ($commentTokens as $commentToken) {

tests/Core/Tokenizer/Comment/SingleLineDocBlockTest.inc

@@ -1,5 +1,8 @@
 <?php
 
+/* testEmptyBlockCommentNoWhiteSpace */
+/**/
+
 /* testEmptyDocblockWithWhiteSpace */
 /** */
 

tests/Core/Tokenizer/Comment/SingleLineDocBlockTest.php

@@ -58,6 +58,26 @@ public static function dataDocblockOpenerCloser()
     }//end dataDocblockOpenerCloser()
 
 
+    /**
+     * Verify an empty block comment is tokenized as T_COMMENT, not as a docblock.
+     *
+     * @covers PHP_CodeSniffer\Tokenizers\PHP::tokenize
+     *
+     * @return void
+     */
+    public function testEmptyBlockCommentNoWhiteSpace()
+    {
+        $expectedSequence = [
+            [T_COMMENT => '/**/'],
+        ];
+
+        $target = $this->getTargetToken('/* '.__FUNCTION__.' */', [T_COMMENT, T_DOC_COMMENT_OPEN_TAG]);
+
+        $this->checkTokenSequence($target, $expectedSequence);
+
+    }//end testEmptyBlockCommentNoWhiteSpace()
+
+
     /**
      * Verify tokenization of an empty, single line DocBlock.
      *