read a consistent amount from pointer file

A few places were reading the max symlink size of a pointer file,
then passing tp parseLinkTargetOrPointer. Which is fine currently, but
to support pointer files with lines of data after the pointer, enough
has to be read that parseLinkTargetOrPointer can be assured of seeing
enough of that data to know if it's correctly formatted.

Sponsored-by: Dartmouth College's Datalad project

Database/Keys.hs

@@ -447,7 +447,7 @@ reconcileStaged qh = unlessM (Git.Config.isBare <$> gitRepo) $ do
 	  where
 		procthread mdreader catfeeder = mdreader >>= \case
 			Just (ka, Just (sha, size, _type))
-				| size < maxPointerSz -> do
+				| size < fromIntegral maxPointerSz -> do
 					() <- catfeeder (ka, sha)
 					procthread mdreader catfeeder
 			Just _ -> procthread mdreader catfeeder