build(broccoli-typescript): check for map files before deleting them

fixes #5610
Closes #6065

tools/broccoli/broccoli-typescript.ts

@@ -212,7 +212,10 @@ class DiffingTSCompiler implements DiffingBroccoliPlugin {
 
     if (fs.existsSync(absoluteJsFilePath)) {
       fs.unlinkSync(absoluteJsFilePath);
+      if (fs.existsSync(absoluteMapFilePath)) {
+        // source map could be inline or not generated
         fs.unlinkSync(absoluteMapFilePath);
+      }
       fs.unlinkSync(absoluteDtsFilePath);
     }
   }