mercurial/cacheutil.py

lazymanifest: avoid reading uninitialized memory

I got errors running tests with clang UBSAN [1] enabled. One of them is:

```
--- test-dirstate.t
+++ test-dirstate.t.err
@@ -85,9 +85,115 @@
   $ echo "[extensions]" >> .hg/hgrc
   $ echo "dirstateex=../dirstateexception.py" >> .hg/hgrc
   $ hg up 0
-  abort: simulated error while recording dirstateupdates
-  [255]
+  mercurial/cext/manifest.c:781:13: runtime error: load of value 190, which is not a valid value for type 'bool'
+      #0 0x7f668a8cf748 in lazymanifest_diff mercurial/cext/manifest.c:781
+      #1 0x7f6692fc1dc4 in call_function Python-2.7.11/Python/ceval.c:4350
+      .......
+  SUMMARY: UndefinedBehaviorSanitizer: invalid-bool-load mercurial/cext/manifest.c:781:13 in
+  [1]
   $ hg log -r . -T '{rev}\n'
   1
   $ hg status
-  ? a
```

While the code is not technically wrong, but switching the condition would
make clang UBSAN happy. So let's do it.

The uninitialized memory could come from, for example, `lazymanifest_copy`
allocates `self->maxlines` items but only writes the first `self->lines`
items.

[1]: https://clang.llvm.org/docs/UndefinedBehaviorSanitizer.html

Test Plan:
Run `test-dirstate.t` with UBSAN and it no longer reports the issue.

Differential Revision: https://phab.mercurial-scm.org/D1948

# scmutil.py - Mercurial core utility functions
#
#  Copyright Matt Mackall <[e-mail]> and other
#
# This software may be used and distributed according to the terms of the
# GNU General Public License version 2 or any later version.
from __future__ import absolute_import

from . import repoview

def cachetocopy(srcrepo):
    """return the list of cache file valuable to copy during a clone"""
    # In local clones we're copying all nodes, not just served
    # ones. Therefore copy all branch caches over.
    cachefiles = ['branch2']
    cachefiles += ['branch2-%s' % f for f in repoview.filtertable]
    cachefiles += ['rbc-names-v1', 'rbc-revs-v1']
    cachefiles += ['tags2']
    cachefiles += ['tags2-%s' % f for f in repoview.filtertable]
    cachefiles += ['hgtagsfnodes1']
    return cachefiles