up2k-snap-load: assert .PARTIAL for unfinished

when loading up2k snaps, entries are forgotten if
the relevant file has been deleted since last run

when the entry is an unfinished upload, the file that should
be asserted is the .PARTIAL, and not the placeholder / final
filename (which, unintentionally, was the case until now)

if .PARTIAL is missing but the placeholder still exists,
the only safe alternative is to forget/disown the file,
since its state is obviously wrong and unknown

copyparty/up2k.py

@@ -1119,6 +1119,7 @@ def register_vpath(
         reg = {}
         drp = None
         emptylist = []
+        dotpart = "." if self.args.dotpart else ""
         snap = os.path.join(histpath, "up2k.snap")
         if bos.path.exists(snap):
             with gzip.GzipFile(snap, "rb") as f:
@@ -1131,25 +1132,31 @@ def register_vpath(
             except:
                 pass
 
+            reg = reg2  # diff-golf
+
             if reg2 and "dwrk" not in reg2[next(iter(reg2))]:
                 for job in reg2.values():
                     job["dwrk"] = job["wark"]
 
             rm = []
             for k, job in reg2.items():
                 job["ptop"] = ptop
-                if "done" in job:
+                is_done = "done" in job
+                if is_done:
                     job["need"] = job["hash"] = emptylist
                 else:
                     if "need" not in job:
                         job["need"] = []
                     if "hash" not in job:
                         job["hash"] = []
 
-                fp = djoin(ptop, job["prel"], job["name"])
+                if is_done:
+                    fp = djoin(ptop, job["prel"], job["name"])
+                else:
+                    fp = djoin(ptop, job["prel"], dotpart + job["name"] + ".PARTIAL")
+
                 if bos.path.exists(fp):
-                    reg[k] = job
-                    if "done" in job:
+                    if is_done:
                         continue
                     job["poke"] = time.time()
                     job["busy"] = {}