Fix linker's handling of malformed function references.

pkg/analyzer/lib/src/summary/link.dart

Index: pkg/analyzer/lib/src/summary/link.dart
diff --git a/pkg/analyzer/lib/src/summary/link.dart b/pkg/analyzer/lib/src/summary/link.dart
index 87af2c0a22a6ed992dce8d3ac63d7f0bbbb83873..fa924dca1183f4a34318349e03e5934a0646558c 100644
--- a/pkg/analyzer/lib/src/summary/link.dart
+++ b/pkg/analyzer/lib/src/summary/link.dart
@@ -1002,7 +1002,8 @@ abstract class CompilationUnitElementForLink
         if (linkedReference.kind == ReferenceKind.function) {
           // Local function
           _references[index] = _resolveRef(containingReference)
-              .getLocalFunction(linkedReference.localIndex);
+                  .getLocalFunction(linkedReference.localIndex) ??
+              UndefinedElementForLink.instance;
         } else {
           _references[index] =
               _resolveRef(containingReference).getContainedName(name);