go/zodb/btree: Fix missing return on data-consistency error

staticcheck reports

    ziobtree.go:606:4: Errorf is a pure function but its return value is ignored (SA4017)
    ziobtree.go:626:4: Errorf is a pure function but its return value is ignored (SA4017)
    zlobtree.go:606:4: Errorf is a pure function but its return value is ignored (SA4017)
    zlobtree.go:626:4: Errorf is a pure function but its return value is ignored (SA4017)

go/zodb/btree/btree.go.in

 // Copyright (c) 2001, 2002 Zope Foundation and Contributors.
 // All Rights Reserved.
 //
-// Copyright (C) 2018-2019  Nexedi SA and Contributors.
+// Copyright (C) 2018-2021  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This software is subject to the provisions of the Zope Public License,
@@ -601,7 +601,7 @@ func (bt *btreeState) PySetState(pystate interface{}) (err error) {
 		}
 
 		if i > 1 && !(key > kprev) {
-			fmt.Errorf("data: [%d]: key not ↑", i)
+			return fmt.Errorf("data: [%d]: key not ↑", i)
 		}
 		kprev = key
 
@@ -621,7 +621,7 @@ func (bt *btreeState) PySetState(pystate interface{}) (err error) {
 			childrenKind = kind
 		}
 		if kind != childrenKind {
-			fmt.Errorf("data: [%d]: children must be of the same type", i)
+			return fmt.Errorf("data: [%d]: children must be of the same type", i)
 		}
 
 		bt.data = append(bt.data, Entry{key: kkey, child: child.(Node)})

go/zodb/btree/ziobtree.go

@@ -3,7 +3,7 @@
 // Copyright (c) 2001, 2002 Zope Foundation and Contributors.
 // All Rights Reserved.
 //
-// Copyright (C) 2018-2019  Nexedi SA and Contributors.
+// Copyright (C) 2018-2021  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This software is subject to the provisions of the Zope Public License,
@@ -603,7 +603,7 @@ func (bt *iobtreeState) PySetState(pystate interface{}) (err error) {
 		}
 
 		if i > 1 && !(key > kprev) {
-			fmt.Errorf("data: [%d]: key not ↑", i)
+			return fmt.Errorf("data: [%d]: key not ↑", i)
 		}
 		kprev = key
 
@@ -623,7 +623,7 @@ func (bt *iobtreeState) PySetState(pystate interface{}) (err error) {
 			childrenKind = kind
 		}
 		if kind != childrenKind {
-			fmt.Errorf("data: [%d]: children must be of the same type", i)
+			return fmt.Errorf("data: [%d]: children must be of the same type", i)
 		}
 
 		bt.data = append(bt.data, IOEntry{key: kkey, child: child.(IONode)})

go/zodb/btree/zlobtree.go

@@ -3,7 +3,7 @@
 // Copyright (c) 2001, 2002 Zope Foundation and Contributors.
 // All Rights Reserved.
 //
-// Copyright (C) 2018-2019  Nexedi SA and Contributors.
+// Copyright (C) 2018-2021  Nexedi SA and Contributors.
 //                          Kirill Smelkov <kirr@nexedi.com>
 //
 // This software is subject to the provisions of the Zope Public License,
@@ -603,7 +603,7 @@ func (bt *lobtreeState) PySetState(pystate interface{}) (err error) {
 		}
 
 		if i > 1 && !(key > kprev) {
-			fmt.Errorf("data: [%d]: key not ↑", i)
+			return fmt.Errorf("data: [%d]: key not ↑", i)
 		}
 		kprev = key
 
@@ -623,7 +623,7 @@ func (bt *lobtreeState) PySetState(pystate interface{}) (err error) {
 			childrenKind = kind
 		}
 		if kind != childrenKind {
-			fmt.Errorf("data: [%d]: children must be of the same type", i)
+			return fmt.Errorf("data: [%d]: children must be of the same type", i)
 		}
 
 		bt.data = append(bt.data, LOEntry{key: kkey, child: child.(LONode)})