fgetc() returns int, not char.

This has no practical effect, since this code doesn't actually need to
distinguish EOF (-1) from \0377; but it silences a Coverity complaint.

src/backend/utils/activity/pgstat.c

@@ -1498,7 +1498,7 @@ pgstat_read_statsfile(void)
 	 */
 	for (;;)
 	{
-		char		t = fgetc(fpin);
+		int			t = fgetc(fpin);
 
 		switch (t)
 		{