pam-util: fix pam_syslog_pam_error() format string

To cut off a string at some position we must set the "precision" not the
field width in format strings.

This led to some assert()s being hit where they really should not be.

(cherry picked from commit f200d6c)
(cherry picked from commit 1c47432)

Author: poettering

src/shared/pam-util.c

@@ -37,7 +37,8 @@ int pam_syslog_pam_error(pam_handle_t *handle, int level, int error, const char
                         pamerr = "n/a";  /* We cannot have any formatting chars */
 
                 char buf[p - format + strlen(pamerr) + 1];
-                xsprintf(buf, "%*s%s", (int)(p - format), format, pamerr);
+                xsprintf(buf, "%.*s%s", (int)(p - format), format, pamerr);
+
                 DISABLE_WARNING_FORMAT_NONLITERAL;
                 pam_vsyslog(handle, level, buf, ap);
                 REENABLE_WARNING;