Fix NPE in BridgeContext.obtainStyledAttributes() [DO NOT MERGE]

Replace direct member access with getter that checks for nullness.

Change-Id: I4a56a0ee903ae7d8c89b91d74b128302e1965586
(cherry picked from commit d758e042ce)

tools/layoutlib/bridge/src/com/android/layoutlib/bridge/android/BridgeContext.java

@@ -127,6 +127,7 @@ public final class BridgeContext extends Context {
         new IdentityHashMap<Object, Map<String,String>>();
 
     // maps for dynamically generated id representing style objects (StyleResourceValue)
+    @Nullable
     private Map<Integer, StyleResourceValue> mDynamicIdToStyleMap;
     private Map<StyleResourceValue, Integer> mStyleToDynamicIdMap;
     private int mDynamicIdGenerator = 0x02030000; // Base id for R.style in custom namespace
@@ -695,7 +696,7 @@ public final class BridgeContext extends Context {
                 }
             }
         } else if (defStyleRes != 0) {
-            StyleResourceValue item = mDynamicIdToStyleMap.get(defStyleRes);
+            StyleResourceValue item = getStyleByDynamicId(defStyleRes);
             if (item != null) {
                 defStyleValues = item;
             } else {