Minor performance tweak

Author: MarkBaker

src/PhpSpreadsheet/Worksheet/Validations.php

@@ -42,10 +42,9 @@ public static function validateCellAddress($cellAddress): string
     public static function validateCellOrCellRange($cellRange): string
     {
         if (is_string($cellRange) || is_numeric($cellRange)) {
-            // Convert a single column reference like 'A' to 'A:A'
-            $cellRange = (string) preg_replace('/^([A-Z]+)$/', '${1}:${1}', (string) $cellRange);
-            // Convert a single row reference like '1' to '1:1'
-            $cellRange = (string) preg_replace('/^(\d+)$/', '${1}:${1}', $cellRange);
+            // Convert a single column reference like 'A' to 'A:A',
+            //    a single row reference like '1' to '1:1'
+            $cellRange = (string) preg_replace('/^([A-Z]+|\d+)$/', '${1}:${1}', (string) $cellRange);
         } elseif (is_object($cellRange) && $cellRange instanceof CellAddress) {
             $cellRange = new CellRange($cellRange, $cellRange);
         }