Add stack handling sanity checks

lib/handlebars/compiler/javascript-compiler.js

@@ -1,4 +1,5 @@
 import { COMPILER_REVISION, REVISION_CHANGES, log } from "../base";
+import Exception from "../exception";
 
 function Literal(value) {
   this.value = value;
@@ -104,6 +105,10 @@ JavaScriptCompiler.prototype = {
     // Flush any trailing content that might be pending.
     this.pushSource('');
 
+    if (this.stackSlot || this.inlineStack.length || this.compileStack.length) {
+      throw new Exception('Compile completed with content left on stack');
+    }
+
     return this.createFunctionContext(asObject);
   },
 
@@ -771,6 +776,9 @@ JavaScriptCompiler.prototype = {
       return item.value;
     } else {
       if (!inline) {
+        if (!this.stackSlot) {
+          throw new Exception('Invalid stack pop');
+        }
         this.stackSlot--;
       }
       return item;