Restore psql's SIGPIPE setting if popen() fails.

Ancient oversight in PageOutput(): if popen() fails, we'd better reset
the SIGPIPE handler before returning stdout, because ClosePager() won't.
Noticed while fixing the empty-PAGER issue.

src/bin/psql/print.c

@@ -2880,6 +2880,8 @@ PageOutput(int lines, const printTableOpt *topt)
 			pagerpipe = popen(pagerprog, "w");
 			if (pagerpipe)
 				return pagerpipe;
+			/* if popen fails, silently proceed without pager */
+			restore_sigpipe_trap();
 		}
 	}