add: respect --ignore-errors when lstat() reports errors

"git add --ignore-errors" command fails immediately when lstat returns an error, despite the ignore errors' flag is enabled.

There could be files that triggers an error on stat(), when other files proceed correctly. Issue can be reproduced when running git under Cygwin and some target files have utf-8 long names (200+ utf chars). Windows can handle them, but all operations on them failed under Cygwin. Issue can not be reproduced with usual latin/numeric only names. For example, create a file with 220 'й' letters by Windows Explorer, then in Cygwin:

Here and below "ййй..." means the line of й copied 220 times.
=============================================================

$ echo -n 'ййй...' | wc -c # check the real size 440

$ ls -la ls: cannot access 'ййй...'$'\320': No such file or directory
-????????? ? ? ? ? ? 'ййй...'$'\320'

$ ls й* ls: cannot access 'ййй...'$'\320': No such file or directory

$ stat й* stat: cannot stat 'ййй...'$'\320': No such file or directory

In my perspective, it's okay to skip these problematic files when ignore error flag is specified, but official Git terminates entire git add command when such files come up. But with proposed patch it is the desired behavior:

$ git add --ignore-errors . error: ййй... can only add regular files,
symbolic links or git-directories

All other files have been added correctly.
==========================================

qusielle (1):
add: respect --ignore-errors when lstat() reports errors

 read-cache.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

base-commit: 566a1439f6f56c2171b8853ddbca0ad3f5098770
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-432%2Fqusielle%2Fmaster-v2
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-432/qusielle/master-v2
Pull-Request: https://github.com/gitgitgadget/git/pull/432

Range-diff vs v1:

1: fd022f88f5 ! 1: d88ea544d9 add: respect --ignore-errors when lstat() reports errors

     @@ -46,7 +46,13 @@
       {
       	struct stat st;
      -	if (lstat(path, &st))
     -+	if (lstat(path, &st) && !(flags & ADD_CACHE_IGNORE_ERRORS))
     - 		die_errno(_("unable to stat '%s'"), path);
     +-		die_errno(_("unable to stat '%s'"), path);
     ++	if (lstat(path, &st)) {
     ++		if (flags & ADD_CACHE_IGNORE_ERRORS)
     ++			return -1;
     ++		else
     ++			die_errno(_("unable to stat '%s'"), path);
     ++	}
       	return add_to_index(istate, path, &st, flags);
       }
     + 

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