Prevent overflow in calculation of strsize for [lookup]parameters (#1550)
Prevent overflow in calculation of strsize for [lookup]parameters (#1550)

The integer calculation otherwise overflows before conversion to a size_t, resulting in bad values being written to serialized models.
shuheik/dynet,danielhers/dynet,danielhers/dynet,shuheik/dynet,clab/dynet,clab/dynet,shuheik/dynet,shuheik/dynet,danielhers/dynet,danielhers/dynet,shuheik/dynet,danielhers/dynet,clab/dynet,clab/dynet,danielhers/dynet,shuheik/dynet,danielhers/dynet,clab/dynet,shuheik/dynet,clab/dynet,clab/dynet