Fix empty labels (#383)

We actually need this `;` for EmptyStatement, otherwise it applies to the next block of code. (Creating a label with an empty statement is completely useless, but it triggers a lot in the fuzz testing tool)

Fixes #376

src/printer.js

@@ -921,6 +921,13 @@ function genericPrintNoParens(path, options, print) {
 
       return concat(parts);
     case "LabeledStatement":
+      if (n.body.type === "EmptyStatement") {
+        return concat([
+          path.call(print, "label"),
+          ":;"
+        ]);
+      }
+
       return concat([
         path.call(print, "label"),
         ":",

tests/label/__snapshots__/jsfmt.spec.js.snap

@@ -0,0 +1,8 @@
+exports[`test empty_label.js 1`] = `
+"a:;
+b
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+a:;
+b;
+"
+`;

tests/label/empty_label.js

@@ -0,0 +1,2 @@
+a:;
+b

tests/label/jsfmt.spec.js

@@ -0,0 +1 @@
+run_spec(__dirname);