fix: Make sure to pass non-empty strings to SpiderBits\Dom

\DOMDocument::loadHTML fails if an empty string is passed.
It's pretty strange as the documentation says it only generates a
warning.

Nevertheless, it's way better to make sure to always pass non-empty
strings to it.

lib/SpiderBits/src/Dom.php

@@ -19,6 +19,8 @@ class Dom
 
     /**
      * Return a new Dom object from text.
+     *
+     * @param non-empty-string $html_as_string
      */
     public static function fromText(string $html_as_string, int $libxml_options = 0): self
     {

lib/SpiderBits/src/Response.php

@@ -89,6 +89,10 @@ public function encoding(): string
             return $charset;
         }
 
+        if (!$data) {
+            return 'utf-8';
+        }
+
         $result = preg_match(
             '/^\s*<\?xml\s+(?:(?:.*?)\s)?encoding=[\'"](?P<encoding>.+?)[\'"]/i',
             $data,

src/services/FeedFetcher.php

@@ -251,6 +251,10 @@ public function fetch(models\Collection $collection): void
 
             $data = $response->utf8Data();
 
+            if (!$data) {
+                return;
+            }
+
             $dom = \SpiderBits\Dom::fromText($data);
             $url_illustration = \SpiderBits\DomExtractor::illustration($dom);
             $url_illustration = \SpiderBits\Url::sanitize($url_illustration);
@@ -373,6 +377,11 @@ public function fetchUrl(string $url): array
             return $info; // @codeCoverageIgnore
         }
 
+        if (!$data) {
+            $info['error'] = 'Empty content';
+            return $info;
+        }
+
         try {
             $feed = \SpiderBits\feeds\Feed::fromText($data);
             $info['feed'] = $feed;

src/services/LinkFetcher.php

@@ -245,6 +245,10 @@ public function fetchUrl(string $url): array
             return $info; // @codeCoverageIgnore
         }
 
+        if (!$data) {
+            return $info;
+        }
+
         $dom = \SpiderBits\Dom::fromText($data);
 
         // Parse the title from the DOM