Merge branch 'B8149ExcelExportcutoffatColumnAA' into 'master'

Fixes #8149 Excel Export cutoff at Column AA

See merge request !136

extension/Source/core/report/Excel.php

@@ -173,24 +173,16 @@ class Excel {
     }
 
     /**
-     * Increment the alpha string. If 'Z' is reached on the last position, it appends 'A'.
+     * Increment the alpha string. i.e. count using A-Z as base.
      * 'A' > 'B'
-     * 'Z' > 'ZA'
-     * 'ZA' > 'ZB'
+     * 'Z' > 'AA'
+     * 'AA' > 'AB'
+     * 'AGTC' > 'AGTD'
      *
      * @param $column
      * @return string - incremented column.
      */
     private function nextColumn($column) {
-        $len = strlen($column);
-        $c = $column[$len - 1];
-        if ($c == 'Z') {
-            $column .= 'A';
-        } else {
-            $c = ++$c;
-            $column[$len - 1] = $c;
-        }
-
-        return $column;
+        return ++$column;
     }
 }