(extend_face_to_end_of_line): Always add space glyph to

(extend_face_to_end_of_line): Always add space glyph to
empty row.  Fixes memory corruption revealed by 2006-03-02 change.
(display_tool_bar_line): Skip empty tool-bar line if HEIGHT < 0.
(tool_bar_lines_needed): Fix tool-bar display in case the tool-bar
width is exactly the same as the window width.  Don't count a final
empty tool-bar line (pass HEIGHT = -1 to display_tool_bar_line).