Set each cell to '?' for testing purposes

Each cell of a console is initialized to '?' to allow testing the glyph
operations.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>

src/console.c

@@ -294,6 +294,7 @@ int kmscon_console_resize(struct kmscon_console *con, uint32_t x, uint32_t y)
 				kmscon_char_free(cells[j].ch);
 			goto err_free;
 		}
+		kmscon_char_set_u8(cells[i].ch, "?", 1);
 	}
 
 	kmscon_font_unref(con->font);