Fixed BUG#4941: Stored procedure crash fetching null value into variable.

mysql-test/r/sp.result:
  New test case for BUG#4941.
mysql-test/t/sp.test:
  New test case for BUG#4941.
sql/protocol_cursor.cc:
  Handle null values.
sql/sp_rcontext.cc:
  Handle null values.

mysql-test/r/sp.result

@@ -1833,6 +1833,22 @@ NULL
 Warnings:
 Warning	1311	Referring to uninitialized variable v
 drop function bug4487|
+drop procedure if exists bug4941|
+create procedure bug4941(out x int)
+begin
+declare c cursor for select i from t2 limit 1;
+open c;
+fetch c into x;
+close c;
+end|
+insert into t2 values (null, null, null)|
+set @x = 42|
+call bug4941(@x)|
+select @x|
+@x
+NULL
+delete from t1|
+drop procedure bug4941|
 drop table if exists fac|
 create table fac (n int unsigned not null primary key, f bigint unsigned)|
 create procedure ifac(n int unsigned)

mysql-test/t/sp.test

@@ -2000,6 +2000,28 @@ select bug4487()|
 drop function bug4487|
 
 
+#
+# BUG#4941: Stored procedure crash fetching null value into variable.
+#
+--disable_warnings
+drop procedure if exists bug4941|
+--enable_warnings
+create procedure bug4941(out x int)
+begin
+  declare c cursor for select i from t2 limit 1;
+  open c;
+  fetch c into x;
+  close c;
+end|
+
+insert into t2 values (null, null, null)|
+set @x = 42|
+call bug4941(@x)|
+select @x|
+delete from t1|
+drop procedure bug4941|
+
+
 #
 # Some "real" examples
 #

sql/protocol_cursor.cc

@@ -112,7 +112,8 @@ bool Protocol_cursor::write()
 
   for (; cur_field < fields_end; ++cur_field, ++data_tmp)
   {
-    if ((len= net_field_length((uchar **)&cp)) == 0)
+    if ((len= net_field_length((uchar **)&cp)) == 0 ||
+	len == NULL_LENGTH)
     {
       *data_tmp= 0;
     }

sql/sp_rcontext.cc

@@ -230,6 +230,9 @@ sp_cursor::fetch(THD *thd, List<struct sp_pvar> *vars)
       return -1;
     }
     s= row[fldcount];
+    if (!s)
+      it= new Item_null();
+    else
       switch (sp_map_result_type(pv->type))
       {
       case INT_RESULT: