Store treebuilder length separately from entries vec

The treebuilder entries vector flags removed items which means
we can't rely on the entries vector length to accurately get the
number of entries.  This adds an entrycount value and maintains it
while updating the treebuilder entries.

src/tree.c

@@ -355,7 +355,7 @@ size_t git_tree_entrycount(const git_tree *tree)
 unsigned int git_treebuilder_entrycount(git_treebuilder *bld)
 {
 	assert(bld);
-	return (int)bld->entries.length;
+	return (unsigned int)bld->entrycount;
 }
 
 static int tree_error(const char *str, const char *path)
@@ -453,6 +453,7 @@ static int append_entry(
 	if (git_vector_insert(&bld->entries, entry) < 0)
 		return -1;
 
+	bld->entrycount++;
 	return 0;
 }
 
@@ -642,14 +643,18 @@ int git_treebuilder_insert(
 
 	if (!tree_key_search(&pos, &bld->entries, filename, strlen(filename))) {
 		entry = git_vector_get(&bld->entries, pos);
-		if (entry->removed)
+		if (entry->removed) {
 			entry->removed = 0;
+			bld->entrycount++;
+		}
 	} else {
 		entry = alloc_entry(filename);
 		GITERR_CHECK_ALLOC(entry);
 
 		if (git_vector_insert(&bld->entries, entry) < 0)
 			return -1;
+
+		bld->entrycount++;
 	}
 
 	git_oid_cpy(&entry->oid, id);
@@ -691,6 +696,7 @@ int git_treebuilder_remove(git_treebuilder *bld, const char *filename)
 		return tree_error("Failed to remove entry. File isn't in the tree", filename);
 
 	remove_ptr->removed = 1;
+	bld->entrycount--;
 	return 0;
 }
 
@@ -747,8 +753,10 @@ void git_treebuilder_filter(
 
 	for (i = 0; i < bld->entries.length; ++i) {
 		git_tree_entry *entry = bld->entries.contents[i];
-		if (!entry->removed && filter(entry, payload))
+		if (!entry->removed && filter(entry, payload)) {
 			entry->removed = 1;
+			bld->entrycount--;
+		}
 	}
 }
 
@@ -763,6 +771,7 @@ void git_treebuilder_clear(git_treebuilder *bld)
 	}
 
 	git_vector_clear(&bld->entries);
+	bld->entrycount = 0;
 }
 
 void git_treebuilder_free(git_treebuilder *bld)

src/tree.h

@@ -27,6 +27,7 @@ struct git_tree {
 
 struct git_treebuilder {
 	git_vector entries;
+	size_t entrycount; /* vector may contain "removed" entries */
 };
 
 GIT_INLINE(int) git_tree__dup(git_tree **dest, git_tree *source)