Update vl_covdet.c
Update vl_covdet.c

Fix a memory leak.

hongzhili/vlfeat,CansenJIANG/vlfeat,CansenJIANG/vlfeat,hongzhili/vlfeat,richarddzh/vlfeat,WangDequan/vlfeat,cvfish/vlfeat,WangDequan/vlfeat,richarddzh/vlfeat,mylxiaoyi/vlfeat,rxl194/vlfeat,cvfish/vlfeat,rxl194/vlfeat,hongzhili/vlfeat,WangDequan/vlfeat,WangDequan/vlfeat,mylxiaoyi/vlfeat,CansenJIANG/vlfeat,cvfish/vlfeat,qubick/vlfeat,rxl194/vlfeat,qubick/vlfeat,j-bo/vlfeat,cvfish/vlfeat,qubick/vlfeat,erexhepa/vlfeat,rxl194/vlfeat,vlfeat/vlfeat,j-bo/vlfeat,j-bo/vlfeat,richarddzh/vlfeat,j-bo/vlfeat,hongzhili/vlfeat,hongzhili/vlfeat,mylxiaoyi/vlfeat,richarddzh/vlfeat,mylxiaoyi/vlfeat,vlfeat/vlfeat,CansenJIANG/vlfeat,erexhepa/vlfeat,cvfish/vlfeat,erexhepa/vlfeat,rxl194/vlfeat,WangDequan/vlfeat,vlfeat/vlfeat,richarddzh/vlfeat,richarddzh/vlfeat,CansenJIANG/vlfeat,WangDequan/vlfeat,erexhepa/vlfeat,erexhepa/vlfeat,vlfeat/vlfeat,j-bo/vlfeat,qubick/vlfeat,erexhepa/vlfeat,vlfeat/vlfeat,vlfeat/vlfeat,CansenJIANG/vlfeat,hongzhili/vlfeat,qubick/vlfeat,mylxiaoyi/vlfeat,rxl194/vlfeat,mylxiaoyi/vlfeat,cvfish/vlfeat,qubick/vlfeat