Don't rename duplicate folders (fixes #1675)

Renaming them puts the user in a difficult situation as they can't
rename them back in the GUI. This way, they need to fix the config in
the same way it got broken (manual editing or external tool).

internal/config/config.go

@@ -9,7 +9,6 @@ package config
 
 import (
 	"encoding/xml"
-	"fmt"
 	"io"
 	"math/rand"
 	"os"
@@ -310,7 +309,6 @@ func (cfg *Configuration) prepare(myID protocol.DeviceID) {
 
 	// Check for missing, bad or duplicate folder ID:s
 	var seenFolders = map[string]*FolderConfiguration{}
-	var uniqueCounter int
 	for i := range cfg.Folders {
 		folder := &cfg.Folders[i]
 
@@ -339,15 +337,8 @@ func (cfg *Configuration) prepare(myID protocol.DeviceID) {
 
 		if seen, ok := seenFolders[folder.ID]; ok {
 			l.Warnf("Multiple folders with ID %q; disabling", folder.ID)
-
 			seen.Invalid = "duplicate folder ID"
-			if seen.ID == folder.ID {
-				uniqueCounter++
-				seen.ID = fmt.Sprintf("%s~%d", folder.ID, uniqueCounter)
-			}
 			folder.Invalid = "duplicate folder ID"
-			uniqueCounter++
-			folder.ID = fmt.Sprintf("%s~%d", folder.ID, uniqueCounter)
 		} else {
 			seenFolders[folder.ID] = folder
 		}