Fix TokensList::getPrevious which was not able to reach very first token

Author: Tithugues

src/TokensList.php

@@ -119,7 +119,7 @@ public function getNext()
      */
     public function getPrevious(): ?Token
     {
-        for (; $this->idx > 0; --$this->idx) {
+        for (; $this->idx >= 0; --$this->idx) {
             if (
                 ($this->tokens[$this->idx]->type !== Token::TYPE_WHITESPACE)
                 && ($this->tokens[$this->idx]->type !== Token::TYPE_COMMENT)

tests/Lexer/TokensListTest.php

@@ -79,6 +79,7 @@ public function testGetPrevious(): void
         $this->assertEquals($this->tokens[6], $list->getPrevious());
         $this->assertEquals($this->tokens[4], $list->getPrevious());
         $this->assertEquals($this->tokens[2], $list->getPrevious());
+        $this->assertEquals($this->tokens[0], $list->getPrevious());
         $this->assertNull($list->getPrevious());
     }