Fixed occasionally seg fault when printing String Values

When the *class_def_item.source_file_idx is 0xffffffff, the NO_INDEX value it produces the seg fault. I just add a quick check to print it or not.

//printStringValue(string_id_list,*class_def_item.source_file_idx,input,str,"%s\n"); causes a seg fault on some dex files

H.