Ensure isDegenerate can be called for all entities

modules/osm/entity.js

@@ -153,6 +153,9 @@ osmEntity.prototype = {
         return false;
     },
 
+    isDegenerate: function() {
+        return true;
+    },
 
     deprecatedTags: function() {
         var tags = _.toPairs(this.tags);

modules/osm/node.js

@@ -36,6 +36,15 @@ _.extend(osmNode.prototype, {
     },
 
 
+    isDegenerate: function() {
+        return !(
+            Array.isArray(this.loc) && this.loc.length === 2 &&
+            this.loc[0] >= -180 && this.loc[0] <= 180 &&
+            this.loc[1] >= -90 && this.loc[1] <= 90
+        );
+    },
+
+
     isIntersection: function(resolver) {
         return resolver.transient(this, 'isIntersection', function() {
             return resolver.parentWays(this).filter(function(parent) {