[BUGFIX] Fix issue parrot#942

io_readline_encoded_string() used to wait for max_bytes_per_codepoint
bytes, which is 4 in case of UTF-8.

However, as UTF-8 is variable-length, there's no guarantee that we'll actually
receive that many bytes and we might hang until the stream gets closed.

src/io/utilities.c

@@ -421,7 +421,10 @@ io_readline_encoded_string(PARROT_INTERP, ARGMOD(PMC *handle),
     if (encoding == NULL)
         encoding = io_get_encoding(interp, handle, vtable, PIO_F_READ);
 
-    if (available_bytes < delim_size || available_bytes < encoding->max_bytes_per_codepoint)
+    /* FIXME: available_bytes < delim_size only makes sense if the
+              encodings agree
+    */
+    if (available_bytes < delim_size || available_bytes < encoding->bytes_per_unit)
         available_bytes = Parrot_io_buffer_fill(interp, buffer, handle, vtable);
 
     s->encoding = encoding;