MDEV-14623: Output of show function code does not show FETCH GROUP NEXT ROW for custom aggregates

The print() function was missing from the FETCH GROUP NEXT ROW instrunction class, so there was no
output for this particular instruction when we use the query SHOW FUNCTION CODE function_name

mysql-test/main/sp-code.result

@@ -1301,3 +1301,24 @@ Pos	Instruction
 28	jump 4
 29	cpop 1
 DROP PROCEDURE p1;
+#
+# MDEV-14623: Output of show function code does not show FETCH GROUP NEXT ROW
+# for custom aggregates
+#
+create aggregate function f1(x INT) returns int
+begin
+declare continue handler for not found return 0;
+loop
+fetch group next row;
+insert into t2 (sal) values (x);
+end loop;
+end|
+show function code f1;
+Pos	Instruction
+0	hpush_jump 2 1 CONTINUE
+1	freturn int 0
+2	agg_cfetch
+3	stmt 5 "insert into t2 (sal) values (x)"
+4	jump 2
+5	hpop 1
+drop function f1;

mysql-test/main/sp-code.test

@@ -927,3 +927,22 @@ $$
 DELIMITER ;$$
 SHOW PROCEDURE CODE p1;
 DROP PROCEDURE p1;
+
+--echo #
+--echo # MDEV-14623: Output of show function code does not show FETCH GROUP NEXT ROW
+--echo # for custom aggregates
+--echo #
+
+delimiter |;
+create aggregate function f1(x INT) returns int
+begin
+  declare continue handler for not found return 0;
+  loop
+    fetch group next row;
+    insert into t2 (sal) values (x);
+  end loop;
+end|
+
+delimiter ;|
+show function code f1;
+drop function f1;

sql/sp_head.cc

@@ -4409,7 +4409,7 @@ sp_instr_cfetch::print(String *str)
 int
 sp_instr_agg_cfetch::execute(THD *thd, uint *nextp)
 {
-  DBUG_ENTER("sp_instr_cfetch::execute");
+  DBUG_ENTER("sp_instr_agg_cfetch::execute");
   int res= 0;
   if (!thd->spcont->instr_ptr)
   {
@@ -4434,7 +4434,16 @@ sp_instr_agg_cfetch::execute(THD *thd, uint *nextp)
   DBUG_RETURN(res);
 }
 
+void
+sp_instr_agg_cfetch::print(String *str)
+{
+
+  uint rsrv= SP_INSTR_UINT_MAXLEN+11;
 
+  if (str->reserve(rsrv))
+    return;
+  str->qs_append(STRING_WITH_LEN("agg_cfetch"));
+}
 
 /*
   sp_instr_cursor_copy_struct class functions

sql/sp_head.h

@@ -1957,7 +1957,7 @@ class sp_instr_agg_cfetch : public sp_instr
 
   virtual int execute(THD *thd, uint *nextp);
 
-  virtual void print(String *str){};
+  virtual void print(String *str);
 }; // class sp_instr_agg_cfetch : public sp_instr