megacli: Fixed handling of multiple Virtual Drive without name

Example configuration where check_raid.pl did not work: 

```
[root@SERVER:~]# MegaCli64 -LdInfo -Lall -aALL -NoLog


Adapter 0 -- Virtual Drive Information:
Virtual Drive: 0 (Target Id: 0)
Name                :
RAID Level          : Primary-1, Secondary-0, RAID Level Qualifier-0
Size                : 135.972 GB
State               : Optimal
Stripe Size         : 128 KB
Number Of Drives    : 2
Span Depth          : 1
Default Cache Policy: WriteBack, ReadAheadNone, Direct, No Write Cache if Bad BBU
Current Cache Policy: WriteBack, ReadAheadNone, Direct, No Write Cache if Bad BBU
Access Policy       : Read/Write
Disk Cache Policy   : Disabled
Encryption Type     : None


Virtual Drive: 1 (Target Id: 1)
Name                :
RAID Level          : Primary-1, Secondary-0, RAID Level Qualifier-0
Size                : 135.972 GB
State               : Optimal
Stripe Size         : 128 KB
Number Of Drives    : 2
Span Depth          : 1
Default Cache Policy: WriteBack, ReadAheadNone, Direct, No Write Cache if Bad BBU
Current Cache Policy: WriteBack, ReadAheadNone, Direct, No Write Cache if Bad BBU
Access Policy       : Read/Write
Disk Cache Policy   : Disabled
Encryption Type     : None


Virtual Drive: 2 (Target Id: 2)
Name                :
RAID Level          : Primary-1, Secondary-0, RAID Level Qualifier-0
Size                : 135.972 GB
State               : Optimal
Stripe Size         : 128 KB
Number Of Drives    : 2
Span Depth          : 1
Default Cache Policy: WriteBack, ReadAheadNone, Direct, No Write Cache if Bad BBU
Current Cache Policy: WriteBack, ReadAheadNone, Direct, No Write Cache if Bad BBU
Access Policy       : Read/Write
Disk Cache Policy   : Disabled
Encryption Type     : None
```

```
[root@SERVER:~]# /usr/local/nagios/libexec/check_raid.pl.ORG -p megacli
OK: megacli:[Volumes(1): NoName:Optimal; Devices(6): 11,10,09,08,12,13=Online]
```