[Yaml] Fixed infinite loop when parser goes through an additional and invalid closing tag

Instead of letting the parser goes in an infinite loop, throw an exception when the additional and invalid is found

src/Symfony/Component/Yaml/Parser.php

@@ -1225,6 +1225,10 @@ class Parser
         $offset = $cursor;
         $cursor += strcspn($this->currentLine, '[]{},: ', $cursor);
 
+        if ($cursor === $offset) {
+            throw new ParseException('Malformed unquoted YAML string.');
+        }
+
         return substr($this->currentLine, $offset, $cursor - $offset);
     }
 

src/Symfony/Component/Yaml/Tests/ParserTest.php

@@ -2676,6 +2676,25 @@ YAML;
         );
     }
 
+    public function testThrowExceptionIfInvalidAdditionalClosingTagOccurs()
+    {
+        $yaml = '{
+            "object": {
+                    "array": [
+                        "a",
+                        "b",
+                        "c"
+                    ]
+                ],
+            }
+        }';
+
+        $this->expectException(ParseException::class);
+        $this->expectExceptionMessage('Malformed unquoted YAML string at line 8 (near "                ],").');
+
+        $this->parser->parse($yaml);
+    }
+
     public function testWhitespaceAtEndOfLine()
     {
         $yaml = "\nfoo:\n    arguments: [ '@bar' ]  \n";