Fix off-by-one, adjust changelog, move scroll keys to consistent place

Ref #1748

docs/changelog.txt

@@ -42,6 +42,7 @@ changelog.txt uses a syntax similar to RST, with a few special sequences:
 - `stockflow`: fixed ``j`` character being intercepted when naming stockpiles
 
 ## Misc Improvements
+- Lua label widgets (used in all standard message boxes) are now scrollable with Up/Down/PgUp/PgDn keys
 - `autofarm`: now fallows farms if all plants have reached the desired count
 - `buildingplan`: set global settings from the ``DFHack#`` prompt: e.g.  ``buildingplan set boulders false``
 - `buildingplan`: add 'enable all' option for buildingplan (so you don't have to enable all building types individually). this setting is not persisted (just like quickfort_mode is not persisted), but it can be set from onMapLoad.init
@@ -55,9 +56,6 @@ changelog.txt uses a syntax similar to RST, with a few special sequences:
 ## Documentation
 - Added documentation for Lua's ``dfhack.run_command()`` and variants
 
-## Misc Improvements
-- Lua widget library Label class (used in all standard message boxes) is now scrollable with Up/Down/PgUp/PgDn keys
-
 # 0.47.04-r4
 
 ## Fixes

library/lua/gui/widgets.lua

@@ -29,6 +29,20 @@ local function map_opttab(tab,idx)
     end
 end
 
+STANDARDSCROLL = {
+    STANDARDSCROLL_UP = -1,
+    STANDARDSCROLL_DOWN = 1,
+    STANDARDSCROLL_PAGEUP = '-page',
+    STANDARDSCROLL_PAGEDOWN = '+page',
+}
+
+SECONDSCROLL = {
+    SECONDSCROLL_UP = -1,
+    SECONDSCROLL_DOWN = 1,
+    SECONDSCROLL_PAGEUP = '-page',
+    SECONDSCROLL_PAGEDOWN = '+page',
+}
+
 ------------
 -- Widget --
 ------------
@@ -344,13 +358,6 @@ end
 
 Label = defclass(Label, Widget)
 
-STANDARDSCROLL = {
-    STANDARDSCROLL_UP = -1,
-    STANDARDSCROLL_DOWN = 1,
-    STANDARDSCROLL_PAGEUP = '-page',
-    STANDARDSCROLL_PAGEDOWN = '+page',
-}
-
 Label.ATTRS{
     text_pen = COLOR_WHITE,
     text_dpen = COLOR_DARKGREY, -- disabled
@@ -414,7 +421,7 @@ end
 
 function Label:scroll(nlines)
     local n = self.start_line_num + nlines
-    n = math.min(n, self:getTextHeight() - self.frame_body.height)
+    n = math.min(n, self:getTextHeight() - self.frame_body.height + 1)
     n = math.max(n, 1)
     self.start_line_num = n
 end
@@ -447,13 +454,6 @@ end
 
 List = defclass(List, Widget)
 
-SECONDSCROLL = {
-    SECONDSCROLL_UP = -1,
-    SECONDSCROLL_DOWN = 1,
-    SECONDSCROLL_PAGEUP = '-page',
-    SECONDSCROLL_PAGEDOWN = '+page',
-}
-
 List.ATTRS{
     text_pen = COLOR_CYAN,
     cursor_pen = COLOR_LIGHTCYAN,