Add null check for classNode.anns to avoid possible NPE

Summary:
In an app that recently crashed appsweep, it happens that one class (`ve5`) has a dex annotation wherein it declares that another class (`ue5`) is a member class. This makes Dex2Pro set `ve5` as the enclosing class of `ue5`.
Later, when it tries to parse annotations for `ue5`, it assumes that the annotations are not `null`, as it is an inner class and as such is expected (but apparently not required by the specification) to have the according annotations. However, `ue5` does not declare any annotations, which in turn causes the null pointer.

This diff introduces a null check that avoids the `NullPointerException`. With the null check, Dex2Pro would remove ue5 from the list of ve5 's inner classes, which seems like sensible behavior to me.

Author: DoHuberGS

android/src/main/java/proguard/dexfile/converter/Dex2Pro.java

@@ -530,7 +530,7 @@ private void convertClass(int dexVersion, DexClassNode classNode, ClassVisitor c
         if (clzInfo != null) {
 //            isInnerClass = clzInfo.enclosingClass != null || clzInfo.enclosingMethod != null;
             if (clzInfo.enclosingClass != null || clzInfo.enclosingMethod != null) {
-                if (classNode.anns.stream().noneMatch(x ->
+                if (classNode.anns != null && classNode.anns.stream().noneMatch(x ->
                         x.type.equals("Ldalvik/annotation/EnclosingMethod;"))) {
                     isInnerClass = true;
                 } else if (clzInfo.enclosingClass != null) {