disallow selection.style as a getter in strict-d3

Author: alexcjohnson

test/image/strict-d3.js

@@ -32,6 +32,10 @@ selProto.style = function() {
 
     if(sel.size()) {
         if(typeof obj === 'string') {
+            if(arguments.length === 1) {
+                throw new Error('d3 selection.style called as getter: ' +
+                    'disallowed as it can fail for unattached elements');
+            }
             checkStyleVal(sel, obj, arguments[1]);
         } else {
             Object.keys(obj).forEach(function(key) { checkStyleVal(sel, key, obj[key]); });