String array attribute leads to segfault in C API

Created by: pnorbert

The conversion routine from char** to string vector in adios2_c_io.cpp:296-310 adios2_define_variable_attribute() is faulty. A test code in C

char *strarray[] = {"first", "second", "third", "fourth"}; adios2_define_attribute(ioH, "strarray", adios2_type_string_array, strarray, 4);

leads to segmentation fault. The incoming const void * pointer should be cast to const char ** then there is a constructor for string vectors for char**, or a simple loop over the pointer can be used.