Do not 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

@@ -156,12 +156,10 @@ public function evictAll(): bool
     {
         // The check below is necessary because on some platforms glob returns false
         // when nothing matched (even though no errors occurred)
-        $filenames = glob(sprintf('%s/*.%s', $this->directory, self::LOCK_EXTENSION));
+        $filenames = glob(sprintf('%s/*.%s', $this->directory, self::LOCK_EXTENSION)) ?: [];
 
-        if ($filenames) {
-            foreach ($filenames as $filename) {
-                @unlink($filename);
-            }
+        foreach ($filenames as $filename) {
+            @unlink($filename);
         }
 
         return $this->region->evictAll();