not a big deal as of now, but once we'll grow the got_object_id struct
it'd be nice to know that all the fields will be zeroed.

ok?

diff /home/op/w/got
commit - 4f152e84c01e22799218a449a85a105ff94fdf9d
path + /home/op/w/got
blob - 8fa42a873d1dd3feb591275a17e1bd546c3dab59
file + lib/object_create.c
--- lib/object_create.c
+++ lib/object_create.c
@@ -198,9 +198,9 @@ got_object_blob_file_create(struct got_object_id **id,
 			break;
 	}
 
-	*id = malloc(sizeof(**id));
+	*id = calloc(1, sizeof(**id));
 	if (*id == NULL) {
-		err = got_error_from_errno("malloc");
+		err = got_error_from_errno("calloc");
 		goto done;
 	}
 	SHA1Final((*id)->sha1, &sha1_ctx);
@@ -392,9 +392,9 @@ got_object_tree_create(struct got_object_id **id,
 		treesize += n;
 	}
 
-	*id = malloc(sizeof(**id));
+	*id = calloc(1, sizeof(**id));
 	if (*id == NULL) {
-		err = got_error_from_errno("malloc");
+		err = got_error_from_errno("calloc");
 		goto done;
 	}
 	SHA1Final((*id)->sha1, &sha1_ctx);
@@ -581,9 +581,9 @@ got_object_commit_create(struct got_object_id **id,
 	}
 	commitsize += n;
 
-	*id = malloc(sizeof(**id));
+	*id = calloc(1, sizeof(**id));
 	if (*id == NULL) {
-		err = got_error_from_errno("malloc");
+		err = got_error_from_errno("calloc");
 		goto done;
 	}
 	SHA1Final((*id)->sha1, &sha1_ctx);
@@ -848,9 +848,9 @@ got_object_tag_create(struct got_object_id **id,
 		tagsize += n;
 	}
 
-	*id = malloc(sizeof(**id));
+	*id = calloc(1, sizeof(**id));
 	if (*id == NULL) {
-		err = got_error_from_errno("malloc");
+		err = got_error_from_errno("calloc");
 		goto done;
 	}
 	SHA1Final((*id)->sha1, &sha1_ctx);