Wrap ClassReferenceInitializer in null check

CallableReferenceInitializer might throw an NPE in ProGuard 8.0.0. It
will be fixed in 8.0.1

Author: mrjameshamilton

src/main/java/proguard/tools/KotlinMetadataPrinter.java

@@ -292,12 +292,19 @@ public void write(int i) { }
 
         // Initialize the other references from the program classes.
         programClassPool.classesAccept(
-            new ClassReferenceInitializer(programClassPool,
-                                          new ClassPool(),
-                                          nullWarningPrinter,
-                                          nullWarningPrinter,
-                                          nullWarningPrinter,
-                                          null));
+            clazz -> {
+                try {
+                    clazz.accept(
+                            new ClassReferenceInitializer(programClassPool,
+                            new ClassPool(),
+                            nullWarningPrinter,
+                            nullWarningPrinter,
+                            nullWarningPrinter,
+                            null));
+                } catch (Exception ignored) {
+                    // TODO: callable reference initialization may cause NPE, will be fixed in ProGuardCORE 8.0.1
+                }
+            });
     }
 
     private static String metadataKindToString(int k)