Fixed BUG#3287: Stored procedure handler scope outside of begin/end.

Backpatching overwrote already backpatched instructions, which made it
skip the hpop instruction; possibly not only a problem for handlers,
but this is one known case when it happened.

mysql-test/t/sp-error.test

@@ -400,7 +400,7 @@ return (select sum(t.data) from test.t2 t)|
 # BUG#1653
 #
 --disable_warnings
-drop table if exists table_1|
+drop table if exists t3|
 --enable_warnings
 create table t3 (column_1_0 int)|
 
@@ -500,6 +500,37 @@ end case|
 call bug3287(2)|
 drop procedure bug3287|
 
+
+#
+# BUG#3297
+#
+--disable_warnings
+drop table if exists t3|
+--enable_warnings
+create table t3 (s1 int, primary key (s1))|
+insert into t3 values (5),(6)|
+
+create procedure bug3279(out y int) 
+begin
+  declare x int default 0;
+  begin
+    declare exit handler for sqlexception set x = x+1;
+    insert into t3 values (5);
+  end;
+  if x < 2 then
+    set x = x+1;
+    insert into t3 values (6);
+  end if;
+  set y = x;
+end|
+
+set @x = 0|
+--error 1062
+call bug3279(@x)|
+select @x|
+drop procedure bug3279|
+drop table t3|
+
 drop table t1|
 
 delimiter ;|