Don't implicitly cast glob's return type

The comment above mentions that on some platforms, it might return
false, and this is why there is a check in the first place. Let us do
exactly what is mentioned in the comment.

src/Cache/Region/FileLockRegion.php

@@ -158,7 +158,7 @@ public function evictAll(): bool
         // when nothing matched (even though no errors occurred)
         $filenames = glob(sprintf('%s/*.%s', $this->directory, self::LOCK_EXTENSION));
 
-        if ($filenames) {
+        if ($filenames !== false) {
             foreach ($filenames as $filename) {
                 @unlink($filename);
             }