Generic/CallTimePassByReference: fix non-problematic bug

This commit fixes a non-problematic bug when there are only empty tokens
after a variable or string token and nothing else.

Before this commit, the code would search for the next non-empty token
after a variable or string token. It would assume that there would
always be such a token and it would check if this token is a open
parenthesis token. It is possible that there are no tokens or only empty
tokens after the variable or string token when live coding.

This assumption would not cause any problems because when checking if
`$tokens[$openBracket]['code'] !== T_OPEN_PARENTHESIS`, `$openBracket`
would be `false`, and then PHP would check for the first element in the
$tokens array. The first token can never be a T_OPEN_PARENTHESIS and
so the code would bail early as expected.

This commit adds a `$openBracket === false` check to bail early as well
to make it clear that `$openBracket` can be false.

Author: rodrigoprimo

src/Standards/Generic/Sniffs/Functions/CallTimePassByReferenceSniff.php

@@ -69,7 +69,7 @@ public function process(File $phpcsFile, $stackPtr)
             true
         );
 
-        if ($tokens[$openBracket]['code'] !== T_OPEN_PARENTHESIS) {
+        if ($openBracket === false || $tokens[$openBracket]['code'] !== T_OPEN_PARENTHESIS) {
             return;
         }
 

src/Standards/Generic/Tests/Functions/CallTimePassByReferenceUnitTest.2.inc

@@ -0,0 +1,7 @@
+<?php
+
+// Intentional parse error.
+// This should be the only test in this file.
+// Testing that the sniff is *not* triggered when there are only empty tokens after a variable and nothing else.
+
+$var