Description of problem:
unlabeld partition vfat partitions did not appear in gnome
and if the user tries to set a mount point like /media/C or /mnt/C
while installing for a vfat partition that does not have a name an exception will happen

How reproducible:
always

Steps to Reproduce:
1. create a 5GB sparse file name hdd.img 
2. used parted on that file to create 1GB vfat partition without label and leave 4GB unallocated for fedora installation
3. start a qemu virtual machine
4. double click the vfat partition in custom disk layout and set a mount point for it
  
Actual results:
exception dialog

Expected results:
no error

Additional info:
I suggest code like this

def label_gen():
  for j in xrange(67,91): yield chr(j)
  for j in xrange(65,91):
    for i in suffex_gen():
       l=chr(j)+str(i)
       if len(l)>max_l: return None
       yield l

def suggest_name(f,chk):
  for i in label_gen():
     if chk(i): return i
  return None

where max_l could be set to 8
and chk is a function that returns true if the suggested label is ok it could be something like this
if i not in labels: return True