Fix get_visible_line_count in RichTextLabel with newlines

Fixed #59359.

(cherry picked from commit 32cdf9fad2e0cffdc7fb9e4bcce2dedc1ead9f9d)

scene/gui/rich_text_label.cpp

@@ -714,7 +714,6 @@ int RichTextLabel::_process_line(ItemFrame *p_frame, const Vector2 &p_ofs, int &
 
 				if (p_mode != PROCESS_CACHE) {
 					lh = line < l.height_caches.size() ? l.height_caches[line] : 1;
-					line_is_blank = true;
 				}
 
 			} break;