get_visible_line_count() in RichTextLabel is wrong if text contains newlines

[KoBeWi]

Godot version

3.5 beta2

System information

Windows 10 x64

Issue description

When text contains newlines, get_visible_line_count() is off by the number of newlines. I use this code to automatically scroll the RTL:

func _process(delta: float) -> void:
	if visible_characters < text.length():
		visible_characters += 1
	
	if get_visible_line_count() > 6:
		get_v_scroll().value += 3

To the left is text with single, autowrapped line. To the right is text with one newline. The visible line count starts from 0 and is 1 too low.

Does not happen on master.

Steps to reproduce

1. Add RichTextLabel
2. Write some text that wraps
3. Animate visible_characters
4. Check the results of get_visible_line_count()
5. Do the same with text with line breaks

Minimal reproduction project

ReproductionProject.zip

[pfertyk]

Hi! I'd like to submit a solution.

I've removed the code that, if a newline was encountered, would treat the whole line as empty. Possibly there are other dependencies for that calculation that I'm not currently aware of, in which case I'll update my PR.

[akien-mga]

Fixed by #59765.