rasql: segfault with avg_cells on empty collection with complex type

[Bang Pham Huu]

From the collection created in ​http://rasdaman.org/ticket/2065, run this command

select avg_cells(c) from test_CFloat32 as c

Then, it shows a segfault and rasserver killed

ing... [ERROR] - 2019-04-09 17:03:18,458, server/rasserver_main.cc:165: Interrupted by signal SIGSEGV (Invalid memory access at address 0)... stacktrace:
 [1] /lib64/libpthread.so.0(+0xf5e0) [0x7f77740365e0]
 [2] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x690453]
 [3] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x549a34]
 [4] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x5881da]
 [5] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x5b7660]
 [6] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x4a9383]
 [7] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x419bba]
 [8] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x76db2e]
 [9] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x79ed50]
[10] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x794fee]
[11] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x7c4062]
[12] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x7b27ae]
[13] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x7c4097]
[14] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x7b287d]
[15] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x8469ee]
[16] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x848e2b]
[17] /home/rasdaman/rasdaman_community/install/bin/rasserver() [0x848f3c]

[Dimitar Misev]

duplicate of #2111