Return original input when specified range is unformattable (#2250)

* Add failing test for range-formatting whitespace

See https://github.com/prettier/prettier/issues/2247#issue-238322065

* Return original input when specified range is unformattable

Fixes https://github.com/prettier/prettier/issues/2247

index.js

@@ -219,6 +219,14 @@ function calculateRange(text, opts, ast) {
     endNonWhitespace,
     isSourceElement
   );
+
+  if (!startNodeAndParents || !endNodeAndParents) {
+    return {
+      rangeStart: 0,
+      rangeEnd: 0
+    };
+  }
+
   const siblingAncestors = findSiblingAncestors(
     startNodeAndParents,
     endNodeAndParents

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

@@ -223,4 +223,11 @@ catch (err) {}
 try {
 } catch (err) {}
 
+`;
+
+exports[`whitespace.js 1`] = `
+ 
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ 
+
 `;

tests/range/whitespace.js

@@ -0,0 +1 @@
+<<<PRETTIER_RANGE_START>>> <<<PRETTIER_RANGE_END>>>