Return an error response if an error occurs in load

[s-yata]

Description

A load can be represented by more than one lines and each line is passed via grn_ctx_send.
In such a case, errors in earlier lines are logged but may not be included in a response as follows:

> table_create tbl TABLE_NO_KEY
[[0,1456992579.56416,0.00168776512145996],true]

> column_create tbl val COLUMN_SCALAR Int32
[[0,1456992579.56662,0.00175976753234863],true]

> load --table tbl '[["val","no_such_column"],["foo","var"]]'
[[-22,1456992579.56916,0.00114750862121582,"nonexistent column: <no_such_column>",[["bracket_close","db.c",12739],["load.grn",4,"load --table tbl '[[\"val\",\"no_such_column\"],[\"foo\",\"var\"]]'"]]],0]

> load --table tbl
> [
> ["val", "no_such_column"],
> ["foo", "var"]
> ]
[[0,1456992579.57066,0.000158071517944336],0]

The last load should return an error response.

[s-yata]

Now a multi-line load can return an error response as follows:

$ groonga -n /tmp/groonga/db
> table_create tbl TABLE_NO_KEY
[[0,1457321139.90177,0.00135469436645508],true]
> column_create tbl val COLUMN_SCALAR Int32
[[0,1457321139.90378,0.00059819221496582],true]
> load --table tbl '[["val","no_such_column"],["foo","var"]]'
[[-22,1457321139.90568,0.000501155853271484,"nonexistent column: <no_such_column>",
 [["bracket_close","db.c",12761]]],0]
> load --table tbl
> [
> ["val", "no_such_column"],
> ["foo", "var"]
> ]
[[-22,1457321139.90673,0.000919342041015625,"nonexistent column: <no_such_column>",
 [["bracket_close","db.c",12761]]],0]

However, the following example shows a strange behavior.
Only load --table tbl '[["val"],["hoge"],["foo","var"]]' returns an error response.

$ groonga -n /tmp/groonga/db
> table_create tbl TABLE_NO_KEY
[[0,1457321420.91614,0.00125432014465332],true]
> column_create tbl val COLUMN_SCALAR Int32
[[0,1457321420.92137,0.00413870811462402],true]
> load --table tbl '[["val"],["foo","var"],["hoge"]]'
[[0,1457321420.92585,0.000856161117553711],1]
> load --table tbl '[["val"],["hoge"],["foo","var"]]'
[[-22,1457321420.92692,0.000379323959350586,"unexpected #values: expected:1, actual:2",
 [["bracket_close","db.c",12842]]],1]
> load --table tbl
> [
> ["val"],
> ["hoge"],
> ["foo", "var"]
> ]
[[0,1457321420.92739,0.000867128372192383],1]

I'm not sure what is the expected response for each command.