Don't get stuck at "Syncing 0%" when adding a new folder

The number of copiers and pullers is set to default at config loading
time, but the new folder configuration doesn't pass through config
loading so we start up with 0 copiers and 0 pullers and hence get stuck.
I moved the default handling to the puller itself instead. I think this
way is also cleaner as we get to keep the 0 in the config and the puller
gets to decide the defaults on it's own.

gui/syncthing/core/syncthingController.js

@@ -1079,6 +1079,7 @@ angular.module('syncthing.core')
                 selectedDevices: {},
                 rescanIntervalS: 60,
                 minDiskFreePct: 1,
+                order: "random",
                 fileVersioningSelector: "none",
                 trashcanClean: 0,
                 simpleKeep: 5,

lib/config/config.go

@@ -404,12 +404,6 @@ func (cfg *Configuration) prepare(myID protocol.DeviceID) {
 		cfg.Folders[i].Devices = ensureDevicePresent(cfg.Folders[i].Devices, myID)
 		cfg.Folders[i].Devices = ensureExistingDevices(cfg.Folders[i].Devices, existingDevices)
 		cfg.Folders[i].Devices = ensureNoDuplicates(cfg.Folders[i].Devices)
-		if cfg.Folders[i].Copiers == 0 {
-			cfg.Folders[i].Copiers = 1
-		}
-		if cfg.Folders[i].Pullers == 0 {
-			cfg.Folders[i].Pullers = 16
-		}
 		sort.Sort(FolderDeviceConfigurationList(cfg.Folders[i].Devices))
 	}
 

lib/config/config_test.go

@@ -89,8 +89,8 @@ func TestDeviceConfig(t *testing.T) {
 				Devices:         []FolderDeviceConfiguration{{DeviceID: device1}, {DeviceID: device4}},
 				ReadOnly:        true,
 				RescanIntervalS: 600,
-				Copiers:         1,
-				Pullers:         16,
+				Copiers:         0,
+				Pullers:         0,
 				Hashers:         0,
 				AutoNormalize:   true,
 				MinDiskFreePct:  1,

lib/model/rwfolder.go

@@ -66,6 +66,11 @@ const (
 	dbUpdateShortcutFile
 )
 
+const (
+	defaultCopiers = 1
+	defaultPullers = 16
+)
+
 type dbUpdateJob struct {
 	file    protocol.FileInfo
 	jobType int
@@ -102,7 +107,7 @@ type rwFolder struct {
 }
 
 func newRWFolder(m *Model, shortID uint64, cfg config.FolderConfiguration) *rwFolder {
-	return &rwFolder{
+	p := &rwFolder{
 		stateTracker: stateTracker{
 			folder: cfg.ID,
 			mut:    sync.NewMutex(),
@@ -131,6 +136,15 @@ func newRWFolder(m *Model, shortID uint64, cfg config.FolderConfiguration) *rwFo
 
 		errorsMut: sync.NewMutex(),
 	}
+
+	if p.copiers == 0 {
+		p.copiers = defaultCopiers
+	}
+	if p.pullers == 0 {
+		p.pullers = defaultPullers
+	}
+
+	return p
 }
 
 // Helper function to check whether either the ignorePerm flag has been