fix php 7.4 incompatibility issues

Author: saimaz

Service/ExportService.php

@@ -99,7 +99,7 @@ public function exportIndex(
      */
     protected function getFilePath($filename): string
     {
-        if ($filename{0} == '/' || strstr($filename, ':') !== false) {
+        if ($filename[0] == '/' || strstr($filename, ':') !== false) {
             return $filename;
         }
 

Service/ImportService.php

@@ -65,7 +65,7 @@ public function importIndex(
      */
     protected function getFilePath($filename)
     {
-        if ($filename{0} == '/' || strstr($filename, ':') !== false) {
+        if ($filename[0] == '/' || strstr($filename, ':') !== false) {
             return $filename;
         }