Absorb resize events in ptest, rather than advancing. After Bill Gray.

(ERR check to compensate for unexpected behavior with macOS ncurses.)

demos/ptest.c

@@ -51,16 +51,18 @@ void wait_a_while(long msec)
     c = getch();
 
 #ifdef KEY_RESIZE
-    if (c == KEY_RESIZE)
+    while (c == KEY_RESIZE || (msec == 1 && c == ERR))
     {
 # ifdef PDCURSES
         resize_term(0, 0);
 # endif
         sizecheck();
         backfill();
+        pflush();
+        c = getch();
     }
-    else
 #endif
+
     if (c == 'q')
     {
         endwin();