Check if written save files are zero length. Fixes #191

By default, file writing fails aren't detected by Inform. This becomes a problem
if we run out of disk space, because the games allows saving without complaint,
and then the save files will be useless when the player tries to restore.

We fix this by rewriting the save game routine to check that the files aren't 0 length.

Fix provided by Dannii Willis.

Counterfeit Monkey.materials/Extensions/Counterfeit Monkey/Presentation Details.i7x

@@ -822,4 +822,63 @@ To say post-restore routine:
 
 [The last line above will close the graphics window if we have switched off graphics but restore a game made with graphics on. Some interpreters, such as Spatterlight and Zoom, will still show the graphics window for a split-second on restore.]
 
+Section 6 - Check that save file isn't empty
+
+[By default, file writing fails aren't detected by Inform. This becomes a problem if we run out of disk space, because the games allows saving without complaint, and then the save files will be useless when the player tries to restore.
+
+See GitHub issue #191.
+
+We fix this by rewriting the save game routine to check that the files aren't 0 length.
+
+Fix provided by Dannii Willis.]
+
+Include (-
+
+[ SAVE_THE_GAME_R fref len res;
+	if (actor ~= player) rfalse;
+	fref = glk_fileref_create_by_prompt(fileusage_SavedGame, filemode_Write, 0);
+	if (fref) {
+		gg_savestr = glk_stream_open_file(fref, filemode_Write, GG_SAVESTR_ROCK);
+		if (gg_savestr) {
+			@save gg_savestr res;
+			if (res == -1) {
+				! The player actually just typed "restore". We first have to recover
+				! all the Glk objects; the values in our global variables are all wrong.
+				GGRecoverObjects();
+				glk_stream_close(gg_savestr, GLK_NULL);
+				gg_savestr = 0;
+				RESTORE_THE_GAME_RM('B'); new_line;
+				rtrue;
+			}
+			glk_stream_close(gg_savestr, GLK_NULL);
+			gg_savestr = 0;
+			if (res == 0) {
+				! Check that the savefile was actually written - this is mostly to account for browser limits in Parchment
+				if (glk_fileref_does_file_exist(fref)) {
+					gg_savestr = glk_stream_open_file(fref, filemode_Read, GG_SAVESTR_ROCK);
+					if (gg_savestr) {
+						glk_stream_set_position(gg_savestr, 0, seekmode_End);
+						len = glk_stream_get_position(gg_savestr);
+						glk_stream_close(gg_savestr, GLK_NULL);
+						gg_savestr = 0;
+						if (len) {
+							! We've confirmed the file exists and has content, which is about all we can do
+							SAVE_THE_GAME_RM('B'); new_line;
+							glk_fileref_destroy(fref);
+							rtrue;
+						}
+						! Cleanup the empty file
+						glk_fileref_delete_file(fref);
+					}
+				}
+			}
+		}
+		glk_fileref_destroy(fref);
+	}
+	SAVE_THE_GAME_RM('A'); new_line;
+];
+
+-) instead of "Save The Game Rule"in "Glulx.i6t".
+
+
 Presentation Details ends here.