mutt_expand_fmt(): Fix potential read beyond buffer bounds.

--- mutt-1.4.2.2i/muttlib.c

+++ mutt-1.4.2.2i/muttlib.c

@@ -806,6 +808,7 @@ void mutt_expand_fmt (char *dest, size_t destlen, const char *fmt, const char *s

       p += 2;

       last = p;

+      continue;

     }

     else if (p[1] == '%')

       p++;