eval.c: Fix findfile(), :find, gf in :terminal. #6009

Closes #4299

src/nvim/file_search.c

@@ -1370,6 +1370,11 @@ find_file_in_path_option (
   char_u              *buf = NULL;
   int rel_to_curdir;
 
+  if (rel_fname != NULL && path_with_url((const char *)rel_fname)) {
+    // Do not attempt to search "relative" to a URL. #6009
+    rel_fname = NULL;
+  }
+
   if (first == TRUE) {
     /* copy file name into NameBuff, expanding environment variables */
     save_char = ptr[len];