move up template literal simplification logic - fixes #1874

test/core/fixtures/transformation/es6.template-literals/expression-first/actual.js

@@ -6,3 +6,4 @@ const example = `${"a"}`;
 const example2 = `${1}`;
 const example3 = 1 + `${foo}${bar}${baz}`;
 const example4 = 1 + `${foo}bar${baz}`;
+const example5 = `${""}`;

test/core/fixtures/transformation/es6.template-literals/expression-first/expected.js

@@ -8,3 +8,4 @@ var example = "a";
 var example2 = "" + 1;
 var example3 = 1 + ("" + foo + bar + baz);
 var example4 = 1 + (foo + "bar" + baz);
+var example5 = "";