sleep: no blank first line when there is nothing to report before the nap

memo

@@ -389,8 +389,9 @@ def cmd_note(d, args):
 
 
 def cmd_sleep(d, args):
-    T = log_len(d)
+    T, said = log_len(d), False
     if args:
+        said = True
         if len(args) != 2:
             die("usage: memo sleep <lo>-<hi> \"<one line>\"")
         m = re.fullmatch(r"(\d+)-(\d+)", args[0])
@@ -413,7 +414,7 @@ def cmd_sleep(d, args):
     if not nap:
         print("Nothing left to compress.")
         return
-    print("\n" + nap)
+    print(("\n" if said else "") + nap)
 
 
 def cmd_forget(d, args):