Don't write out a null spec

- #1370

brut.apktool/apktool-lib/src/main/java/brut/androlib/res/data/value/ResStyleValue.java

@@ -52,6 +52,11 @@ public class ResStyleValue extends ResBagValue implements
         }
         for (int i = 0; i < mItems.length; i++) {
             ResResSpec spec = mItems[i].m1.getReferent();
+
+            if (spec == null) {
+                continue;
+            }
+
             String name = null;
             String value = null;