### Please describe the problem.
The watcher in `git annex webapp` crashes (see error below).

It seems to be a result of having the file `Icon^M^M` in `.gitignore`


### What steps will reproduce the problem?
1. Add `Icon^M^M` into `.gitignore`
2. Start the webapp
3. See the error in the top right hand side of the screen

### What version of git-annex are you using? On what operating system?

[[!format sh """
git-annex version: 7.20190912
build flags: Assistant Webapp Pairing S3 WebDAV FsEvents TorrentParser MagicMime Feeds Testsuite
dependency versions: aws-0.21.1 bloomfilter-2.0.1.0 cryptonite-0.26 DAV-1.3.3 feed-1.2.0.0 ghc-8.6.5 http-client-0.6.4 persistent-sqlite-2.10.5 torrent-10000.1.1 uuid-1.3.13 yesod-1.6.0
key/value backends: SHA256E SHA256 SHA512E SHA512 SHA224E SHA224 SHA384E SHA384 SHA3_256E SHA3_256 SHA3_512E SHA3_512 SHA3_224E SHA3_224 SHA3_384E SHA3_384 SKEIN256E SKEIN256 SKEIN512E SKEIN512 BLAKE2B256E BLAKE2B256 BLAKE2B512E BLAKE2B512 BLAKE2B160E BLAKE2B160 BLAKE2B224E BLAKE2B224 BLAKE2B384E BLAKE2B384 BLAKE2BP512E BLAKE2BP512 BLAKE2S256E BLAKE2S256 BLAKE2S160E BLAKE2S160 BLAKE2S224E BLAKE2S224 BLAKE2SP256E BLAKE2SP256 BLAKE2SP224E BLAKE2SP224 SHA1E SHA1 MD5E MD5 WORM URL
remote types: git gcrypt p2p S3 bup directory rsync web bittorrent webdav adb tahoe glacier ddar git-lfs hook external
operating system: darwin x86_64
supported repository versions: 7
upgrade supported from repository versions: 0 1 2 3 4 5 6
local repository version: 7
"""]]

Running on MacOS 10.13.6
### Please provide any additional information below.

[[!format sh """
Watcher crashed: unknown response from git cat-file ("HEAD:./Library/Icon missing",Ref "HEAD:./Library/Icon\r")
CallStack (from HasCallStack):
error, called at ./Git/CatFile.hs:119:28 in main:Git.CatFile
"""]]

### Have you had any luck using git-annex before? (Sometimes we get tired of reading bug reports all day and a lil' positive end note does wonders)

Yes!  Been using it since the start.  Donated.  Will donate again if you run a funding run.

> [[fixed|done]] --[[Joey]]
