silence clang warning

src/dump.c:509:3: warning: variable 'result' is used uninitialized whenever switch
      default is taken [-Wsometimes-uninitialized]
  default:
  ^~~~~~~
src/dump.c:512:7: note: uninitialized use occurs here
  if (result < 0) {
      ^~~~~~
src/dump.c:480:13: note: initialize the variable 'result' to silence this warning
  int result;
            ^
             = 0