Add a missing null check on SkyframeLookupResult#getOrThrow

Speculative fix for bazelbuild#22066

Closes bazelbuild#26101.

PiperOrigin-RevId: 765255882
Change-Id: I7569c3b2175d3bca527673f8aa13d1649c86942a

Author: fmeum

src/main/java/com/google/devtools/build/lib/skyframe/StarlarkBuildSettingsDetailsFunction.java

@@ -163,6 +163,9 @@ private static ImmutableMap<PackageIdentifier, PackageValue> getBuildSettingPack
       for (PackageIdentifier packageKey : packageKeys) {
         try {
           SkyValue skyValue = newlyLoaded.getOrThrow(packageKey, NoSuchPackageException.class);
+          if (skyValue == null) {
+            return null;
+          }
           buildSettingPackages.put(packageKey, (PackageValue) skyValue);
         } catch (NoSuchPackageException e) {
           throw new TransitionException(e);