bugfix: cb_adf is not including some examples in stats calculation

test/RunTests

@@ -1632,3 +1632,7 @@ echo "1 | feature:1" | {VW} -a --initial_weight 0.1 --initial_t 0.3
 # Test 174 cbify adf, regcbopt
 {VW} --cbify 10 --cb_explore_adf --cb_type mtr --regcbopt --mellowness 0.01 -d train-sets/multiclass
     train-sets/ref/cbify_regcbopt.stderr
+
+# Test 175 cb_adf, sharedfeatures
+{VW}  --dsjson --cb_adf -d train-sets/no_shared_features.json
+    train-sets/ref/no_shared_features.stderr

test/train-sets/no_shared_features.json

@@ -0,0 +1 @@
+{"_label_cost":0,"_label_probability":0.333333343,"_label_Action":2,"_labelIndex":1,"o":[{"EventId":"f5547244f88543d1bcad0e3416fbd592","v":{"reward":0.0,"value4":0.0,"value1":0.0,"value2":1400.0,"value3":0.0}}],"Timestamp":"2018-11-22T02:31:39.1440000Z","Version":"1","EventId":"f5547244f88543d1bcad0e3416fbd592","a":[2,1,3],"c":{"_multi":[{"name3":{"name4":4.65312243,"name2":1.0}},{"name3":{"name":4.65312243,"name2":1.0}},{"name3":{"name5":4.65312243}}]},"p":[0.333333343,0.333333343,0.333333343],"VWState":{"m":"N/A"}}

test/train-sets/ref/no_shared_features.stderr

@@ -0,0 +1,17 @@
+Num weight bits = 18
+learning rate = 0.5
+initial_t = 0
+power_t = 0.5
+using no cache
+Reading datafile = train-sets/no_shared_features.json
+num sources = 1
+average  since         example        example  current  current  current
+loss     last          counter         weight    label  predict features
+0.000000 0.000000            1            1.0    known        0:0...        8
+
+finished run
+number of examples = 1
+weighted example sum = 1.000000
+weighted label sum = 0.000000
+average loss = 0.000000
+total feature number = 8

vowpalwabbit/cb_adf.cc

@@ -232,7 +232,7 @@ bool update_statistics(vw& all, cb_adf& c, example& ec, multi_ex* ec_seq)
 
 void output_example(vw& all, cb_adf& c, example& ec, multi_ex* ec_seq)
 {
-  if (example_is_newline(ec) || (CB::ec_is_example_header(ec) && ec_seq->size() == 1)) return;
+  if (example_is_newline_not_header(ec)) return;
 
   bool labeled_example = update_statistics(all, c, ec, ec_seq);