fix some overflows

src/menu.rs

@@ -24,6 +24,8 @@ pub struct Line {
     link: usize, // link #, if any
 }
 
+const SCROLL_LINES: usize = 15;
+
 impl View for MenuView {
     fn render(&self, cols: usize, rows: usize) -> String {
         self.render_lines(cols, rows)
@@ -128,8 +130,9 @@ impl MenuView {
     }
 
     fn action_page_down(&mut self) -> Action {
-        if self.scroll < self.lines().len() - 15 {
-            self.scroll += 15;
+        let lines = self.lines().len();
+        if lines > SCROLL_LINES && self.scroll < lines - SCROLL_LINES {
+            self.scroll += SCROLL_LINES;
             Action::Redraw
         } else {
             Action::None
@@ -138,8 +141,9 @@ impl MenuView {
 
     fn action_page_up(&mut self) -> Action {
         if self.scroll > 0 {
-            self.scroll -= 15;
-            if self.scroll < 0 {
+            if self.scroll > SCROLL_LINES {
+                self.scroll -= SCROLL_LINES;
+            } else {
                 self.scroll = 0;
             }
             Action::Redraw

src/text.rs

@@ -22,8 +22,12 @@ impl View for TextView {
                 Action::Redraw
             }
             Key::Char('b') | Key::Char('G') => {
-                self.scroll = self.lines - SCROLL_LINES;
-                Action::Redraw
+                if self.lines >= SCROLL_LINES {
+                    self.scroll = self.lines - SCROLL_LINES;
+                    Action::Redraw
+                } else {
+                    Action::None
+                }
             }
             Key::Down => {
                 if self.scroll < self.lines - 1 {
@@ -43,8 +47,9 @@ impl View for TextView {
             }
             Key::PageUp | Key::Char('-') => {
                 if self.scroll > 0 {
-                    self.scroll -= SCROLL_LINES;
-                    if self.scroll < 0 {
+                    if self.scroll >= SCROLL_LINES {
+                        self.scroll -= SCROLL_LINES;
+                    } else {
                         self.scroll = 0;
                     }
                     Action::Redraw
@@ -53,10 +58,13 @@ impl View for TextView {
                 }
             }
             Key::PageDown | Key::Char(' ') => {
-                if self.scroll < self.lines - 1 - SCROLL_LINES {
-                    self.scroll += SCROLL_LINES;
-                    if self.scroll >= self.lines {
-                        self.scroll = self.lines - 1;
+                let lines = self.lines - 1;
+                if lines > SCROLL_LINES {
+                    if self.scroll < lines - SCROLL_LINES {
+                        self.scroll += SCROLL_LINES;
+                        if self.scroll >= lines {
+                            self.scroll = lines;
+                        }
                     }
                     Action::Redraw
                 } else {