journald: do not strip leading whitespace from messages

Keep leading whitespace for compatibility with older syslog
implementations.  Also useful when piping formatted output to the
`logger` command.  Keep removing trailing whitespace.

Tested with `pstree | logger` and checking that the output of
`journalctl | tail` included aligned and formatted output.

Confirmed that all test cases still pass as expected.

src/journal/journald-syslog.c

@@ -234,7 +234,8 @@ size_t syslog_parse_identifier(const char **buf, char **identifier, char **pid)
         if (t)
                 *identifier = t;
 
-        e += strspn(p + e, WHITESPACE);
+        if (strchr(WHITESPACE, p[e]))
+                e++;
         *buf = p + e;
         return e;
 }