Pass undefined fields to helpers in strict mode

This allows for `{{helper foo}}` to still operate under strict mode when `foo` is not defined on the context. This allows helpers to perform whatever existence checks they please so patterns like `{{#if foo}}{{foo}}{{/if}}` can be used to protect against missing values.

Fixes #1063

lib/handlebars/compiler/javascript-compiler.js

@@ -390,7 +390,7 @@ JavaScriptCompiler.prototype = {
   //
   // Looks up the value of `name` on the current context and pushes
   // it onto the stack.
-  lookupOnContext: function(parts, falsy, scoped) {
+  lookupOnContext: function(parts, falsy, strict, scoped) {
     let i = 0;
 
     if (!scoped && this.options.compat && !this.lastContext) {
@@ -401,7 +401,7 @@ JavaScriptCompiler.prototype = {
       this.pushContext();
     }
 
-    this.resolvePath('context', parts, i, falsy);
+    this.resolvePath('context', parts, i, falsy, strict);
   },
 
   // [lookupBlockParam]
@@ -424,19 +424,19 @@ JavaScriptCompiler.prototype = {
   // On stack, after: data, ...
   //
   // Push the data lookup operator
-  lookupData: function(depth, parts) {
+  lookupData: function(depth, parts, strict) {
     if (!depth) {
       this.pushStackLiteral('data');
     } else {
       this.pushStackLiteral('this.data(data, ' + depth + ')');
     }
 
-    this.resolvePath('data', parts, 0, true);
+    this.resolvePath('data', parts, 0, true, strict);
   },
 
-  resolvePath: function(type, parts, i, falsy) {
+  resolvePath: function(type, parts, i, falsy, strict) {
     if (this.options.strict || this.options.assumeObjects) {
-      this.push(strictLookup(this.options.strict, this, parts, type));
+      this.push(strictLookup(this.options.strict && strict, this, parts, type));
       return;
     }