dpkg: Relax --merge-avail Packages file parser to not fail on bogus versions

This makes the behaviour consistent with the other Packages file
action (i.e. --update-avail).

Missed in commit 357ab385750c1cb657ff95c0b34ad0a6bf6d2cdf.

debian/changelog

@@ -57,6 +57,7 @@ dpkg (1.16.2) UNRELEASED; urgency=low
     options. Closes: #367608
   * Improve and clarify dpkg-shlibdeps superfluous linking warning messages.
     Based on a patch by Peter Eisentraut <petere@debian.org>. Closes: #656496
+  * Relax --merge-avail Packages file parser, to not fail on bogus versions.
 
   [ Raphaël Hertzog ]
   * Update Dpkg::Shlibs to look into multiarch paths when cross-building

src/update.c

@@ -87,8 +87,8 @@ updateavailable(const char *const *argv)
 
   if (cipaction->arg_int != act_avclear)
     count += parsedb(sourcefile,
-		     pdb_recordavailable | pdb_rejectstatus | pdb_ignoreolder,
-                     NULL);
+                     pdb_recordavailable | pdb_rejectstatus | pdb_lax_parser |
+                     pdb_ignoreolder, NULL);
 
   if (!f_noact) {
     writedb(availfile, wdb_dump_available);