check_drivesize: fix drives without assigned letters

[inqrphl]

they would have an empty 'name' in their entry data, which resulted in perfdata only having the attribute seemingly without drive name prefix

found and fixed using ai, did not test on the misbehaving system

[lgmu]

Seems to work

Previously:

WARNING - C:\ 70.357 GiB/99.656 GiB (70.6%), F:\ 970.602 MiB/19.983 GiB (4.7%), Z:\ 0 B/0 B (0.0%), System Reserved 33.809 MiB/349.996 MiB (9.7%) |'C:\ used'=75545710592.00B;@70623352504:82393911255;96304571597;0.00;107005079552.00 'C:\ used %'=70.60%;@66:77;90;0.00;100.00 'F:\ used'=1017749504.00B;@14161624351:16521895076;19311305933;0.00;21457006592.00 'F:\ used %'=4.70%;@66:77;90;0.00;100.00 'Z:\ used'=0.00B;@0:0;0;0.00;0.00 'Z:\ used %'=100.00%;@66:77;90;0.00;100.00 ' used'=35450880.00B;@242218353:282588078;330297754;0.00;366997504.00 ' used %'=9.70%;@66:77;90;0.00;100.00

Now:

WARNING - C:\ 70.379 GiB/99.656 GiB (70.6%), F:\ 970.602 MiB/19.983 GiB (4.7%), Z:\ 0 B/0 B (0.0%), System Reserved 33.809 MiB/349.996 MiB (9.7%) |'C:\ used'=75569299456.00B;@70623352504:82393911255;96304571597;0.00;107005079552.00 'C:\ used %'=70.60%;@66:77;90;0.00;100.00 'F:\ used'=1017749504.00B;@14161624351:16521895076;19311305933;0.00;21457006592.00 'F:\ used %'=4.70%;@66:77;90;0.00;100.00 'Z:\ used'=0.00B;@0:0;0;0.00;0.00 'Z:\ used %'=100.00%;@66:77;90;0.00;100.00 'System Reserved used'=35450880.00B;@242218353:282588078;330297754;0.00;366997504.00 'System Reserved used %'=9.70%;@66:77;90;0.00;100.00