tweaks: restore earlier conditions to prevent superfluous redrawings

When doing an <Up> on the top line, or a <Down> on the bottom line of
the edit window, the affected lines have already been redrawn by the
scrolling code, so there is no need to do that again.

(However, that does not prevent the second line (or the last-but-one
line) from being redrawn unnecessarily when using the M-- (or M-+)
command elsewhere on the screen and /that/ line is horizontally
scrolled.  But we'll let that pass for now.)

src/move.c

@@ -439,12 +439,15 @@ void do_up(bool scroll_only)
 #endif
 		editwinrows / 2 + 1);
 
-    /* Redraw the prior line if it was horizontally scrolled. */
-    if (need_horizontal_scroll(was_column, 0))
-	update_line(openfile->current->next, 0);
-    /* Redraw the current line if it needs to be horizontally scrolled. */
-    if (need_horizontal_scroll(0, xplustabs()))
-	update_line(openfile->current, openfile->current_x);
+    /* If the lines weren't already redrawn, see if they need to be. */
+    if (openfile->current_y > 0) {
+	/* Redraw the prior line if it was horizontally scrolled. */
+	if (need_horizontal_scroll(was_column, 0))
+	    update_line(openfile->current->next, 0);
+	/* Redraw the current line if it needs to be horizontally scrolled. */
+	if (need_horizontal_scroll(0, xplustabs()))
+	    update_line(openfile->current, openfile->current_x);
+    }
 }
 
 /* Move up one line. */
@@ -521,12 +524,15 @@ void do_down(bool scroll_only)
 	}
     }
 
-    /* Redraw the prior line if it was horizontally scrolled. */
-    if (need_horizontal_scroll(was_column, 0))
-	update_line(openfile->current->prev, 0);
-    /* Redraw the current line if it needs to be horizontally scrolled. */
-    if (need_horizontal_scroll(0, xplustabs()))
-	update_line(openfile->current, openfile->current_x);
+    /* If the lines weren't already redrawn, see if they need to be. */
+    if (openfile->current_y < editwinrows - 1) {
+	/* Redraw the prior line if it was horizontally scrolled. */
+	if (need_horizontal_scroll(was_column, 0))
+	    update_line(openfile->current->prev, 0);
+	/* Redraw the current line if it needs to be horizontally scrolled. */
+	if (need_horizontal_scroll(0, xplustabs()))
+	    update_line(openfile->current, openfile->current_x);
+    }
 }
 
 /* Move down one line. */