Do not throw on an empty file with a ; (#1503)

Fixes "TypeError: Cannot read property 'replace' of undefined"

This was discovered by #1480 and also affects non-typescript

src/doc-printer.js

@@ -284,10 +284,12 @@ function printDocToString(doc, options) {
                     out.pop();
                   }
 
-                  out[out.length - 1] = out[out.length - 1].replace(
-                    /[^\S\n]*$/,
-                    ""
-                  );
+                  if (out.length) {
+                    out[out.length - 1] = out[out.length - 1].replace(
+                      /[^\S\n]*$/,
+                      ""
+                    );                    
+                  }
                 }
 
                 let length = ind.indent * options.tabWidth + ind.align.spaces;

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

@@ -0,0 +1,8 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`empty.js 1`] = `
+;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+
+`;

tests/empty/empty.js

@@ -0,0 +1 @@
+;

tests/empty/jsfmt.spec.js

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