Walk up data frames for nested @partial-block

The root cause of handlebars-lang#1218 is that `invokePartial` creates a stack of data frames
for nested partial blocks, but `resolvePartial` always uses the value at top of
the stack without "popping" it. The result is an infinite recursive loop, as
references to `@partial-block` in the partial at the top of the stack resolve to
itself.

So, walk up the stack of data frames when evaluating. This is accomplished by
1) setting the `partial-block` property to `noop` after use and
2) using `_parent['partial-block']` if `partial-block` is `noop`

Fix handlebars-lang#1218

lib/handlebars/runtime.js

@@ -197,7 +197,12 @@ export function wrapProgram(container, i, fn, data, declaredBlockParams, blockPa
 export function resolvePartial(partial, context, options) {
   if (!partial) {
     if (options.name === '@partial-block') {
-      partial = options.data['partial-block'];
+      let data = options.data;
+      while (data['partial-block'] === noop) {
+        data = data._parent;
+      }
+      partial = data['partial-block'];
+      data['partial-block'] = noop;
     } else {
       partial = options.partials[options.name];
     }

spec/partials.js

@@ -270,6 +270,20 @@ describe('partials', function() {
         true,
         'success');
     });
+    it('should render nested partial blocks', function() {
+      shouldCompileToWithPartials(
+        '.template-start.{{#> outer}}{{value}}{{/outer}}.template-end.',
+        [
+          {value: 'success'},
+          {},
+          {
+            outer: '.outer-start.{{#> nested}}.outer-partial-block-start.{{> @partial-block}}.outer-partial-block-end.{{/nested}}.outer-end.',
+            nested: '.nested-start.{{> @partial-block}}.nested-end.'
+          }
+        ],
+        true,
+        '.template-start..outer-start..nested-start..outer-partial-block-start.success.outer-partial-block-end..nested-end..outer-end..template-end.');
+    });
   });
 
   describe('inline partials', function() {