Phpstan: fix warnings on sfFileCache and sfMemcache implementation, add missing returns

Author: thePanz

lib/cache/sfFileCache.class.php

@@ -122,6 +122,8 @@ public function removePattern($pattern)
                 @unlink($path);
             }
         }
+
+        return true;
     }
 
     /**

lib/cache/sfMemcacheCache.class.php

@@ -145,6 +145,8 @@ public function clean($mode = sfCache::ALL)
         if (sfCache::ALL === $mode) {
             return $this->memcache->flush();
         }
+
+        return true;
     }
 
     /**
@@ -188,6 +190,8 @@ public function removePattern($pattern)
                 $this->remove(substr($key, strlen($this->getOption('prefix'))));
             }
         }
+
+        return true;
     }
 
     /**