Handle non-empty deleted names bitset

These PDBs ...

UxTheme.pdb/B2CB6C54947E43628848F979CA3D485F2
UxTheme.pdb/CB8F1B2FEF1A4B18B566B1E2A8A9A07B2

... have a non-zero size for the deleted names bitset.  Skip over it as well,
although we have no idea what it means...
Don't fail if there is no stream named '/names'

These PDBs don't seem to have a '/names' stream

user32.pdb/64CB00905BA046E8B021CDD31E8B434F2
user32.pdb/B06717A3E95746C5876CBB90DEA5086B2
user32.pdb/953B04792B8A48B2883930E36FD22A6A2
mswsock.pdb/47409B8D0E6A4DBF8930D24404E9DC1B2
mswsock.pdb/1D73630D03BC4818B6C076DD90AFF58E2
mswsock.pdb/D8F4AC1CDB5846B5B164EDDDF58AAA7F2
ws2_32.pdb/7DC2528E9E7B494694002E18EF00D65A2
ws2_32.pdb/348BE7D22346495B841B7FA203996BD02
kernelbase.pdb/5C8EFE66B1EA441D80F6E43552F28A7F2
kernelbase.pdb/91C72371DD43448192B7B46F5ED10AA02
kernelbase.pdb/88D04DC8E39B4CBB9CB12366C2AE475F2
kernelbase.pdb/0EDDD36C0A824C0A89BB8EE9DA7710F12
kernelbase.pdb/26A0409FBA2049DFB7DC64670E1C502A2
gdi32.pdb/BC8E58D7EB284A218ABB2EBD514180372
advapi32.pdb/699F5B1DC86D40EA9280C58CB9AA46172
kernel32.pdb/2548E2898862444C83BBDFF49AB24F0E2
kernel32.pdb/C4312728BA1F4691955E99B2E026FAFC2
kernel32.pdb/C4D1D9065632419699A8B2F25B62381D2
kernel32.pdb/8CEDA2AECF9A4CCE9DF8600FAF4794FC2
tiptsf.pdb/8F81D68EDD1F40AB8ED26986603804552

In fact, it doesn't look like they have much useful information.  Just warn and
convert what we have, rather than failing