Fix top lines appearing at bottom when resizing a screen that seen more lines than the number of lines available

kitty/rewrap.h

@@ -31,6 +31,7 @@
             linebuf_init_line(dest, dest->ynum - 1); \
             historybuf_add_line(historybuf, dest->line); \
         }\
+        linebuf_clear_line(dest, dest->ynum - 1); \
     } else dest_y++; \
     init_dest_line(dest_y); \
     dest->continued_map[dest_y] = continued;

kitty_tests/screen.py

@@ -246,6 +246,11 @@ def test_resize(self):
         for i in range(s.lines):
             self.ae(str(hb.line(i)), '3')
         self.ae(str(hb.line(5)), '2')
+        s = self.create_screen(scrollback=6)
+        s.draw(''.join([str(i) * s.columns for i in range(s.lines*2)]))
+        self.ae(str(s.line(4)), '9'*5)
+        s.resize(5, 2)
+        self.ae(str(s.line(4)), '9 ')
 
     def test_tab_stops(self):
         # Taken from vttest/main.c