jsonstorage breaks when tuple does not have as many columns as schema

Noticed this error when doing something like
A = flatten(STRSPLIT($0, ',', 3)) AS (col1:chararray, col2:chararray, col3:chararray);
STORE A INTO 'foo' USING JsonStorage();

If the string being split doesn't generate 3 columns, then JsonStorage errors out with an index exception. This is because it tries to read the fields of the tuple passed to it or not. See JsonStorage, line 148.

MY patch checks the length of the tuple. If any schema column positions are past the length of the tuple, it fills in null.