adb: Android serial numbers are not all 16 characters long, so accept other lengths.

I can't find any documentation of how long it should be. Hard to imagine
it being shorter than 4 characters though, so put that in as a conservative
lower bound.

This commit was sponsored by Nick Piper on Patreon.

CHANGELOG

@@ -9,6 +9,8 @@ git-annex (6.20180530) UNRELEASED; urgency=medium
     is configured.
   * External special remotes can now add info to `git annex info $remote`,
     by replying to the GETINFO message.
+  * adb: Android serial numbers are not all 16 characters long, so accept
+    other lengths.
 
  -- Joey Hess <id@joeyh.name>  Wed, 30 May 2018 11:49:08 -0400
 

Remote/Adb.hs

@@ -236,7 +236,7 @@ enumerateAdbConnected =
   where
 	parse l = 
 		let (serial, desc) = separate (== '\t') l
-		in if null desc || length serial /= 16
+		in if null desc || length serial < 4
 			then Nothing 
 			else Just (AndroidSerial serial)
 

doc/bugs/git-annex_doesn__39__t_find_adb_device.mdwn

@@ -20,3 +20,4 @@ git-annex claims that adb does not list any devices. `adb devices` however shows
     upgrade supported from repository versions: 0 1 2 3 4 5
     operating system: linux x86_64
 
+> [[fixed|done]] --[[Joey]] 

doc/bugs/git-annex_doesn__39__t_find_adb_device/comment_1_56070e29ea7f19d24d4ff0f56adf08a0._comment

@@ -0,0 +1,10 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 1"""
+ date="2018-06-12T17:39:51Z"
+ content="""
+It's expecting a serial number 16 digits long, 
+and your adb is using a 12 digit one.  I suppose this means that the length
+can vary. Hopefully because of a difference in the android device and not
+the version of adb. I'll change it to accept shorter serials.
+"""]]