display: make PageUp/PageDown use the correct beginning of the viewport

When typing PageUp or PageDOwn in non-smooth-scrolling mode, the cursor
should be placed at the start of the top line of the edit window.  This
means that, when the line at edittop is partially scrolled offscreen,
the cursor should be placed at openfile->firstcolumn, not at zero.

This fixes https://savannah.gnu.org/bugs/?50645

.
Reported-by: David Lawrence Ramsey <pooka109@gmail.com>

src/move.c

@@ -60,7 +60,8 @@ void do_page_up(void)
      * beginning of the top line of the edit window, as Pico does. */
     if (!ISSET(SMOOTH_SCROLL)) {
 	openfile->current = openfile->edittop;
-	openfile->placewewant = openfile->current_y = 0;
+	openfile->placewewant = target_column = openfile->firstcolumn;
+	openfile->current_y = 0;
     }
 
     mustmove = (editwinrows < 3) ? 1 : editwinrows - 2;
@@ -99,7 +100,8 @@ void do_page_down(void)
      * beginning of the top line of the edit window, as Pico does. */
     if (!ISSET(SMOOTH_SCROLL)) {
 	openfile->current = openfile->edittop;
-	openfile->placewewant = openfile->current_y = 0;
+	openfile->placewewant = target_column = openfile->firstcolumn;
+	openfile->current_y = 0;
     }
 
     mustmove = (editwinrows < 3) ? 1 : editwinrows - 2;