Silence a compiler warning

The compiler doesn't know that `rb_raise` longjmps us out of the
function, so make it feel better by pretending that we'll return a VALUE
no matter what.

Fixes the Clang warning:

  watchman.c:470:1: warning: control may reach end of non-void function [-Wreturn-type]

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

ruby/command-t/watchman.c

@@ -467,6 +467,8 @@ VALUE watchman_load(char **ptr, char *end) {
         default:
             rb_raise(rb_eTypeError, "unsupported type");
     }
+
+    return Qnil; // keep the compiler happy
 }
 
 /**