clone: cleanup the "cleanup dir" logic used during local clone

With the previous code, there was a small windows were we could delete too much
data. This should no longer be the case.

(This is an opportunity improvement while looking at something next to that.)

Differential Revision: https://phab.mercurial-scm.org/D10840

mercurial/hg.py

@@ -825,7 +825,12 b' def clone('
             abspath = os.path.abspath(urlutil.urllocalpath(origsource))
 
         if islocal(dest):
-            cleandir = dest
+            if os.path.exists(dest):
+                # only clean up directories we create ourselves
+                hgdir = os.path.realpath(os.path.join(dest, b".hg"))
+                cleandir = hgdir
+            else:
+                cleandir = dest
 
         copy = False
         if (
@@ -855,9 +860,6 b' def clone('
             hgdir = os.path.realpath(os.path.join(dest, b".hg"))
             if not os.path.exists(dest):
                 util.makedirs(dest)
-            else:
-                # only clean up directories we create ourselves
-                cleandir = hgdir
             try:
                 destpath = hgdir
                 util.makedir(destpath, notindexed=True)