Don't crash initdb when we fail to get the current username.

Give an error message and exit instead, like we do elsewhere...

Per report from Wez Furlong and Robert Treat.

src/bin/initdb/initdb.c

@@ -42,7 +42,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  * Portions taken from FreeBSD.
  *
- * $PostgreSQL: pgsql/src/bin/initdb/initdb.c,v 1.168 2009/02/25 13:03:06 petere Exp $
+ * $PostgreSQL: pgsql/src/bin/initdb/initdb.c,v 1.169 2009/03/31 18:58:16 mha Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -670,6 +670,13 @@ get_id(void)
 				progname);
 		exit(1);
 	}
+	if (!pw)
+	{
+		fprintf(stderr,
+				_("%s: could not obtain information about current user: %s\n"),
+				progname, strerror(errno));
+		exit(1);
+	}
 #else							/* the windows code */
 
 	struct passwd_win32
@@ -681,7 +688,12 @@ get_id(void)
 	DWORD		pwname_size = sizeof(pass_win32.pw_name) - 1;
 
 	pw->pw_uid = 1;
-	GetUserName(pw->pw_name, &pwname_size);
+	if (!GetUserName(pw->pw_name, &pwname_size))
+	{
+		fprintf(stderr, _("%s: could not get current user name: %s\n"),
+				progname, strerror(errno));
+		exit(1);
+	}
 #endif
 
 	return xstrdup(pw->pw_name);