Handle single wrapped line scrolling

Before this change, scrolling down when there were multiple layout lines, that rendered beyond the screen, would not work properly. This is because the current logic only acts if there are two or more buffer lines, calculating the proper layout height for each line.

This adds an edge case check for single lines, ensuring the case is handled.

src/buffer.rs

@@ -343,18 +343,25 @@ impl Buffer {
         } else if let Some(height) = self.height_opt {
             // Adjust scroll forwards if cursor is after it
             let mut line_i = layout_cursor.line;
-            while line_i > self.scroll.line {
-                line_i -= 1;
-                let layout = self
-                    .line_layout(font_system, line_i)
-                    .expect("shape_until_cursor failed to scroll forwards");
-                for layout_line in layout.iter() {
-                    total_height += layout_line.line_height_opt.unwrap_or(metrics.line_height);
-                }
+            if line_i <= self.scroll.line {
+                // This is a single line that may wrap
                 if total_height > height + self.scroll.vertical {
-                    self.scroll.line = line_i;
                     self.scroll.vertical = total_height - height;
                 }
+            } else {
+                while line_i > self.scroll.line {
+                    line_i -= 1;
+                    let layout = self
+                        .line_layout(font_system, line_i)
+                        .expect("shape_until_cursor failed to scroll forwards");
+                    for layout_line in layout.iter() {
+                        total_height += layout_line.line_height_opt.unwrap_or(metrics.line_height);
+                    }
+                    if total_height > height + self.scroll.vertical {
+                        self.scroll.line = line_i;
+                        self.scroll.vertical = total_height - height;
+                    }
+                }
             }
         }