Add defined/property_exists checks to prevent warnings

Author: sirbrillig

VariableAnalysis/Lib/Helpers.php

@@ -385,15 +385,15 @@ public static function findFunctionCallArguments(File $phpcsFile, $stackPtr)
 	/**
 	 * Compatibility handler for phpcs 3.x/4.x
 	 * @param array $tokens
-	 * @param int $tokenIndex
+	 * @param int   $tokenIndex
 	 * @return bool
 	 */
 	private static function hasAssignmentToken($tokens, $tokenIndex)
 	{
-		if (isset(Tokens::ASSIGNMENT_TOKENS[$tokens[$tokenIndex]['code']])) {
+		if (defined('Tokens::ASSIGNMENT_TOKENS') && isset(Tokens::ASSIGNMENT_TOKENS[$tokens[$tokenIndex]['code']])) {
 			return true;
 		}
-		if (isset(Tokens::$assignmentTokens[$tokens[$tokenIndex]['code']])) {
+		if (isset(Tokens::$assignmentTokens) && isset(Tokens::$assignmentTokens[$tokens[$tokenIndex]['code']])) {
 			return true;
 		}
 		return false;