fix inspection of zero

lib/_debugger.js

@@ -561,7 +561,7 @@ Client.prototype.mirrorObject = function(handle, depth, cb) {
     return;
   } else if (handle.type === 'function') {
     val = function() {};
-  } else if (handle.value) {
+  } else if (handle.value !== undefined) {
     val = handle.value;
   } else if (handle.type === 'undefined') {
     val = undefined;