Reproduce failures when using shared babel config to transpile multip…

…le files

```
    TypeError: /Users/rjackson/src/ember-cli/babel-plugin-htmlbars-inline-precompile/foo-bar.js: C
annot read property 'reference' of undefined

      14 |   for (let ref of refPaths) {
      15 |     let binding = ref.scope.getBinding(ref.node.name);
    > 16 |     binding.reference(ref);
         |             ^
      17 |   }
      18 | };
      19 |

      at reference (src/util.js:16:13)
      at registerRefs (index.js:143:7)
      at PluginPass.replacePath (index.js:383:7)
      at newFn (node_modules/@babel/traverse/lib/visitors.js:175:21)

```

Simply guarding for `ref.scope.getBinding(...)` returning `undefined` is
not "good enough".

__tests__/tests.js

@@ -64,6 +64,36 @@ describe('htmlbars-inline-precompile', function () {
     `);
   });
 
+  it('does not error when transpiling multiple modules with a single plugin config', function () {
+    let transpiled = transform(
+      "import hbs from 'htmlbars-inline-precompile';\nvar compiled = hbs`hello`;"
+    );
+
+    expect(transpiled).toMatchInlineSnapshot(`
+      "import { createTemplateFactory as _createTemplateFactory } from \\"@ember/template-factory\\";
+
+      var compiled = _createTemplateFactory(
+      /*
+        hello
+      */
+      \\"precompiled(hello)\\");"
+    `);
+
+    transpiled = transform(
+      "import hbs from 'htmlbars-inline-precompile';\nvar compiled = hbs`hello`;"
+    );
+
+    expect(transpiled).toMatchInlineSnapshot(`
+      "import { createTemplateFactory as _createTemplateFactory } from \\"@ember/template-factory\\";
+
+      var compiled = _createTemplateFactory(
+      /*
+        hello
+      */
+      \\"precompiled(hello)\\");"
+    `);
+  });
+
   it('passes options when used as a call expression', function () {
     let source = 'hello';
     transform(`import hbs from 'htmlbars-inline-precompile';\nvar compiled = hbs('${source}');`);