Fix PHP error with short class names

Author: fredden

Magento2/Sniffs/Less/ClassNamingSniff.php

@@ -66,7 +66,8 @@ public function process(File $phpcsFile, $stackPtr)
                 [implode("", $matches[0])]
             );
         }
-        if (strpos($className, self::STRING_HELPER_CLASSES_PREFIX, 2) !== false) {
+
+        if (strlen($className) > 1 && strpos($className, self::STRING_HELPER_CLASSES_PREFIX, 2) !== false) {
             $phpcsFile->addError(
                 'CSS class names should be separated with "-" (dash) instead of "_" (underscore)',
                 $stackPtr,

Magento2/Tests/Less/ClassNamingUnitTest.less

@@ -30,3 +30,8 @@
 .category-title {
   background: green;
 }
+
+// @see https://github.com/magento/magento-coding-standard/issues/425
+.a {
+  text-decoration: none;
+}