gdatainputstream: Fix length return value on UTF-8 validation failure

The method was correctly returning an error from g_data_input_stream_read_line_utf8() if the line contained invalid UTF-8, but it wasn’t correctly setting the returned line length to 0. This could have caused problems if callers were basing subsequent logic on the length and not the return value nullness or GError.

Signed-off-by: Philip Withnall pwithnall@gnome.org

oss-fuzz#372819437