Fix for bug #8464 (AVG returns incorrect result)

Actually problem was not in AVG function, but in SUM before the AVG in the
query.

mysql-test/r/func_group.result

@@ -832,3 +832,13 @@ id	stddev_pop(value1)	var_pop(value1)	stddev_samp(value1)	var_samp(value1)
 1	0.816497	0.666667	1.000000	1.000000
 2	1.118034	1.250000	1.290994	1.666667
 DROP TABLE t1;
+CREATE TABLE t1 (col1 decimal(16,12));
+INSERT INTO t1 VALUES (-5.00000000001),(-5.00000000002),(-5.00000000003),(-5.00000000000),(-5.00000000001),(-5.00000000002);
+insert into t1 select * from t1;
+select col1,count(col1),sum(col1),avg(col1) from t1 group by col1;
+col1	count(col1)	sum(col1)	avg(col1)
+-5.000000000030	2	-10.000000000060	-5.0000000000300000
+-5.000000000020	4	-20.000000000080	-5.0000000000200000
+-5.000000000010	4	-20.000000000040	-5.0000000000100000
+-5.000000000000	2	-10.000000000000	-5.0000000000000000
+DROP TABLE t1;

mysql-test/t/func_group.test

@@ -537,3 +537,14 @@ CREATE TABLE t1 (id int(11),value1 float(10,2));
 INSERT INTO t1 VALUES (1,0.00),(1,1.00), (1,2.00), (2,10.00), (2,11.00), (2,12.00), (2,13.00);
 select id, stddev_pop(value1), var_pop(value1), stddev_samp(value1), var_samp(value1) from t1 group by id;
 DROP TABLE t1;
+
+#
+# BUG#8464 decimal AVG returns incorrect result
+#
+
+CREATE TABLE t1 (col1 decimal(16,12));
+INSERT INTO t1 VALUES (-5.00000000001),(-5.00000000002),(-5.00000000003),(-5.00000000000),(-5.00000000001),(-5.00000000002);
+insert into t1 select * from t1;
+select col1,count(col1),sum(col1),avg(col1) from t1 group by col1;
+DROP TABLE t1;
+

strings/decimal.c

@@ -1199,7 +1199,10 @@ int decimal2bin(decimal *from, char *to, int precision, int frac)
   else if (fsize0 > fsize1 && frac1x)
   {
     if (frac0 == frac1)
+    {
       frac1x=frac0x;
+      fsize0= fsize1;
+    }
     else
     {
       frac1++;