refactored error handling in LoadKeys()

I2PAddr.go

@@ -71,16 +71,16 @@ func LoadKeys(r string) (I2PKeys, error) {
 	if err != nil {
 		return I2PKeys{}, err
 	}
-	if exists {
+	if !exists {
+		return I2PKeys{}, fmt.Errorf("file does not exist: %s", r)
+	}
 	fi, err := os.Open(r)
 	if err != nil {
-			return I2PKeys{}, err
+		return I2PKeys{}, fmt.Errorf("error opening file: %w", err)
 	}
 	defer fi.Close()
 	return LoadKeysIncompat(fi)
 }
-	return I2PKeys{}, err
-}
 
 // store keys in non standard format
 func StoreKeysIncompat(k I2PKeys, w io.Writer) (err error) {