lib/db, lib/protocol: Never need empty-version entries (fixes #6961) (#6962)

Avoid havoc when discovering locally-deleted-upgraded files during repair / need calculation...

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

lib/protocol/bep_extensions.go

@@ -189,10 +189,6 @@ func WinsConflict(f, other FileIntf) bool {
 	return f.FileVersion().Compare(other.FileVersion()) == ConcurrentGreater
 }
 
-func (f FileInfo) IsEmpty() bool {
-	return f.Version.Counters == nil
-}
-
 func (f FileInfo) IsEquivalent(other FileInfo, modTimeWindow time.Duration) bool {
 	return f.isEquivalent(other, modTimeWindow, false, false, 0)
 }

lib/protocol/vector.go

@@ -127,6 +127,11 @@ func (v Vector) Counter(id ShortID) uint64 {
 	return 0
 }
 
+// IsEmpty returns true when there are no counters.
+func (v Vector) IsEmpty() bool {
+	return len(v.Counters) == 0
+}
+
 // DropOthers removes all counters, keeping only the one with given id. If there
 // is no such counter, an empty Vector is returned.
 func (v Vector) DropOthers(id ShortID) Vector {