Fix potential segfault in RS watchdog.

BUG=5544671

This initializes the watchdog structure properly. Without this fix, it is
possible to call LOGE with a garbage string value.

Change-Id: Ie05eb65f83eca938f18ac962794407d58c3f277f
diff --git a/rsContext.cpp b/rsContext.cpp
index 948ecf9..5291a1f 100644
--- a/rsContext.cpp
+++ b/rsContext.cpp
@@ -359,6 +359,7 @@
     mTargetSdkVersion = 14;
     mDPI = 96;
     mIsContextLite = false;
+    memset(&watchdog, 0, sizeof(watchdog));
 }
 
 Context * Context::createContext(Device *dev, const RsSurfaceConfig *sc) {