Thanks to _that, return null if vector is empty

Change-Id: Idc44455dd0c971c876ae283528c4367a82e145bd
diff --git a/gui/resources.hpp b/gui/resources.hpp
index 3cb5281..54a1185 100644
--- a/gui/resources.hpp
+++ b/gui/resources.hpp
@@ -77,8 +77,8 @@
 	virtual ~AnimationResource();
 
 public:
-	virtual void* GetResource(void) { return mSurfaces.at(0); }
-	virtual void* GetResource(int entry) { return mSurfaces.at(entry); }
+	virtual void* GetResource(void) { return mSurfaces.empty() ? NULL : mSurfaces.at(0); }
+	virtual void* GetResource(int entry) { return mSurfaces.empty() ? NULL : mSurfaces.at(entry); }
 	virtual int GetResourceCount(void) { return mSurfaces.size(); }
 
 protected: