libgfs2: Fix potential NULL deref in linked_leaf_search()
    
    Spotted by coverity: "Null-checking "bh" suggests that it may be null,
    but it has already been dereferenced on all paths leading to the check."
    
    Also remove some dangling whitespace from that function.
    
    Signed-off-by: Andrew Price <anprice@redhat.com>