Silence a Clang warning about use of an uninitialized variable

Silence a Clang warning about use of an uninitialized variable

  parser.c:350:14: warning: variable 'dest' is used uninitialized whenever 'if' condition is false
      else if ((src[0] & 0xf8) == 0xf0)
              ^~~~~~~~~~~~~~~~~~~~~~~
  parser.c:375:12: note: uninitialized use occurs here
      return dest;
            ^~~~
  parser.c:350:10: note: remove the 'if' if its condition is always true
      else if ((src[0] & 0xf8) == 0xf0)
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
  parser.c:307:18: note: initialize the variable 'dest' to silence this warning
      uint32_t dest;
                  ^
                    = 0

In this case the warning is spurious (the `else` branch raises an
exception, so it is not possible for `dest` to be used unuinitialized).
But Clang doesn't know that, so keep it happy by initializing the
variable every time.

Signed-off-by: Wincent Colaiuta <win@wincent.com>