Advances this, calling pred on each character.
If pred returns true, returns true and stops scanning.
If pred never returns true, this is set to limit
if limit is non-null, otherwise to the end iterator.
| this |
a `GtkTextIter` |
| pred |
a function to be called on each character |
| limit |
search limit |
| user_data |
user data for |
|
whether a match was found |