Squiz/ClassFileName: bow out earlier for STDIN

As `STDIN` won't contain a usable file name, bow out and don't examine the input again.

_Note: the `process()` method should really end on a `return $this->phpcsFile->numTokens;` as well as a file containing multiple classes should not get multiple contradicting errors, but that would require each test for this sniff to be in their own file, which I currently don't deem worth the effort._

Author: jrfnl

src/Standards/Squiz/Sniffs/Classes/ClassFileNameSniff.php

@@ -43,13 +43,14 @@ public function register()
      */
     public function process(File $phpcsFile, $stackPtr)
     {
-        $fullPath = basename($phpcsFile->getFilename());
-        $fileName = substr($fullPath, 0, strrpos($fullPath, '.'));
-        if ($fileName === '') {
-            // No filename probably means STDIN, so we can't do this check.
-            return;
+        $filename = $phpcsFile->getFilename();
+        if ($filename === 'STDIN') {
+            return $phpcsFile->numTokens;
         }
 
+        $fullPath = basename($filename);
+        $fileName = substr($fullPath, 0, strrpos($fullPath, '.'));
+
         $tokens  = $phpcsFile->getTokens();
         $decName = $phpcsFile->findNext(T_STRING, $stackPtr);