Fix for bug #1663839: stuttered page down doesn't work if lines are wrapped.
Fix for bug #1663839: stuttered page down doesn't work
if lines are wrapped.

timonwong/foo_uie_wsh_panel_mod.scintilla,timonwong/foo_uie_wsh_panel_mod.scintilla,timonwong/foo_uie_wsh_panel_mod.scintilla,timonwong/foo_uie_wsh_panel_mod.scintilla,timonwong/foo_uie_wsh_panel_mod.scintilla,timonwong/foo_uie_wsh_panel_mod.scintilla,timonwong/foo_uie_wsh_panel_mod.scintilla,timonwong/foo_uie_wsh_panel_mod.scintilla