🐛 Fix error when pass non-string url in fetch()

This commit fixes the error "TypeError: Cannot read properties of
undefined (reading 'split')" which occurs when applying the JavaScript
String split() to the `url` variable that is not a string object.

To prevent this error from occurring, an if-statement has been added to
check the type of the `url` variable and forces the callback return
immediately for non-string values.

This commit addresses issue #82.

src/fetcher.js

@@ -151,6 +151,13 @@ export function fetch(target) {
   // For each media URL
   if (urls != null && urls.length > 0) {
     urls.forEach((url) => {
+
+      // Remove query strings from the URL.
+      if (typeof url !== 'string') {
+        console.warn('The \'url\' variable is not a string.')
+        return;
+      };
+
       // Remove query strings from the URL.
       const pathname = url.split('.com')[1].split('?')[0];
       // Check if the URL appears in the recent logs.