Exclude empty inodes from stats

src/blockstore_init.cpp

@@ -912,7 +912,11 @@ void blockstore_init_journal::erase_dirty_object(blockstore_dirty_db_t::iterator
         ? clean_it->second.location : UINT64_MAX;
     if (exists && clean_loc == UINT64_MAX)
     {
-        bs->inode_space_stats[oid.inode] -= bs->block_size;
+        auto & sp = bs->inode_space_stats[oid.inode];
+        if (sp > bs->block_size)
+            sp -= bs->block_size;
+        else
+            bs->inode_space_stats.erase(oid.inode);
     }
     bs->erase_dirty(dirty_it, dirty_end, clean_loc);
     // Remove it from the flusher's queue, too

src/blockstore_stable.cpp

@@ -200,7 +200,11 @@ void blockstore_impl_t::mark_stable(const obj_ver_id & v, bool forget_dirty)
                 }
                 else if (IS_DELETE(dirty_it->second.state))
                 {
-                    inode_space_stats[dirty_it->first.oid.inode] -= block_size;
+                    auto & sp = inode_space_stats[dirty_it->first.oid.inode];
+                    if (sp > block_size)
+                        sp -= block_size;
+                    else
+                        inode_space_stats.erase(dirty_it->first.oid.inode);
                 }
             }
             if (forget_dirty && (IS_BIG_WRITE(dirty_it->second.state) ||