Fix NPE in NewRepositoryFileHandler

Accidentally introduced in bazelbuild@bf9a3d4.

PiperOrigin-RevId: 671517799
Change-Id: Iea6b372a501fe13390404e7af30f83c22679e809

Author: Wyverald

src/main/java/com/google/devtools/build/lib/rules/repository/NewRepositoryFileHandler.java

@@ -115,11 +115,11 @@ public boolean prepareFile(Rule rule, Environment env)
       } else if (hasFile) {
 
         Pair<RootedPath, FileValue> rootedPathAndFileValue = getFileValue(rule, env);
-        rootedPath = rootedPathAndFileValue.getFirst();
-        fileValue = rootedPathAndFileValue.getSecond();
         if (env.valuesMissing()) {
           return false;
         }
+        rootedPath = rootedPathAndFileValue.getFirst();
+        fileValue = rootedPathAndFileValue.getSecond();
 
       } else if (hasFileContent) {