Don't try to parse 0-length data since TM don't support it

src/document.c

@@ -2260,9 +2260,18 @@ void document_update_tags(GeanyDocument *doc)
 		return;
 	}
 
+	len = sci_get_length(doc->editor->sci);
+	/* tm_source_file_buffer_update() below don't support 0-length data,
+	 * so just empty the tags array and leave */
+	if (len < 1)
+	{
+		tm_tags_array_free(doc->tm_file->tags_array, FALSE);
+		sidebar_update_tag_list(doc, FALSE);
+		return;
+	}
+
 	/* Parse Scintilla's buffer directly using TagManager
 	 * Note: this buffer *MUST NOT* be modified */
-	len = sci_get_length(doc->editor->sci);
 	buffer_ptr = (guchar *) scintilla_send_message(doc->editor->sci, SCI_GETCHARACTERPOINTER, 0, 0);
 	tm_source_file_buffer_update(doc->tm_file, buffer_ptr, len, TRUE);