fix(model): check if remote folder state before pulling files (fixes #9686) (#9732)

### Purpose

As discussed in #9686 
Syncthing currently does not check folderstate on remote device before
pulling. If no devices have a valid folderstate (i.e all devices have
the folder paused) it will still attempt to pull. On large folders this
will cause a hanging "Syncing" status.

This checks whether at least one connected device has the file available
and has a valid folderstate.

### Testing
Tested locally on multiple devices.
We're new to Go (all our stuff is Python) so please bear with!
Interested if there may be a better place to slot this in.

Thanks,
Jon

---------

Co-authored-by: Simon Frei <freisim93@gmail.com>

lib/model/folder_sendrecv.go

@@ -505,13 +505,10 @@ nextFile:
 			continue nextFile
 		}
 
-		devices := snap.Availability(fileName)
-		for _, dev := range devices {
-			if f.model.ConnectedTo(dev) {
-				// Handle the file normally, by copying and pulling, etc.
-				f.handleFile(fi, snap, copyChan)
-				continue nextFile
-			}
+		devices := f.model.fileAvailability(f.FolderConfiguration, snap, fi)
+		if len(devices) > 0 {
+			f.handleFile(fi, snap, copyChan)
+			continue
 		}
 		f.newPullError(fileName, errNotAvailable)
 		f.queue.Done(fileName)
@@ -1547,7 +1544,7 @@ func (f *sendReceiveFolder) pullBlock(state pullBlockState, snap *db.Snapshot, o
 	}
 
 	var lastError error
-	candidates := f.model.availabilityInSnapshot(f.FolderConfiguration, snap, state.file, state.block)
+	candidates := f.model.blockAvailability(f.FolderConfiguration, snap, state.file, state.block)
 loop:
 	for {
 		select {