Fix HTML unparsing when there's no entities

pyrogram/parser/html.py

@@ -233,10 +233,11 @@ def recursive(entity_i: int) -> int:
         while i < len(entities):
             i += recursive(i)
 
-        last_offset = entities_offsets[-1][1]
-        # no need to sort, but still add entities starting from the end
-        for entity, offset in reversed(entities_offsets):
-            text = text[:offset] + entity + html.escape(text[offset:last_offset]) + text[last_offset:]
-            last_offset = offset
+        if entities_offsets:
+            last_offset = entities_offsets[-1][1]
+            # no need to sort, but still add entities starting from the end
+            for entity, offset in reversed(entities_offsets):
+                text = text[:offset] + entity + html.escape(text[offset:last_offset]) + text[last_offset:]
+                last_offset = offset
 
         return utils.remove_surrogates(text)

tests/parser/test_html.py

@@ -137,3 +137,11 @@ def test_html_unparse_escaped_nested():
          pyrogram.types.MessageEntity(type=pyrogram.enums.MessageEntityType.UNDERLINE, offset=8, length=16)])
 
     assert HTML.unparse(text=text, entities=entities) == expected
+
+
+def test_html_unparse_no_entities():
+    expected = "text"
+    text = "text"
+    entities = []
+
+    assert HTML.unparse(text=text, entities=entities) == expected