Fixed casting warnings about copying len into pending buf, replaced with calls to...

Fixed casting warnings about copying len into pending buf, replaced with calls to put_short.

  deflate.c(1413,45): warning C4244: '=': conversion from 'unsigned int' to 'unsigned char', possible loss of data
  deflate.c(1414,50): warning C4244: '=': conversion from 'unsigned int' to 'unsigned char', possible loss of data
  deflate.c(1415,46): warning C4244: '=': conversion from 'unsigned int' to 'unsigned char', possible loss of data
  deflate.c(1416,51): warning C4244: '=': conversion from 'unsigned int' to 'unsigned char', possible loss of data