Improve asserts.

Former-commit-id: f9894c2

Author: jtwigg

cocos2d-ui/CCBReader/CCBReader.m

@@ -690,7 +690,9 @@ - (void) readPropertyForNode:(CCNode*) node parent:(CCNode*)parent isExtraProp:(
         // Load sub file
         NSString* path = [[CCFileUtils sharedFileUtils] fullPathForFilename:ccbFileName];
         NSData* d = [NSData dataWithContentsOfFile:path];
-        
+
+        NSAssert(d,@"Failed to find ccb file: %@",ccbFileName);
+
         CCBReader* reader = [[CCBReader alloc] init];
         reader.animationManager.rootContainerSize = parent.contentSize;