pkgTagFile: if we have seen the end, do not try to see more

Asking for more via Step() will notice that we are done with the file
already and will result in a fail, which means we can't find the last
sections anymore (which is especially painful if we haven't moved at
all as in the testcase we haven't even looked at one of the sources
leading to a strange behaviour)

Reported-By: Niall Walsh <niallwalsh@users.berlios.de>

apt-pkg/tagfile.cc

@@ -207,7 +207,11 @@ bool pkgTagFile::Jump(pkgTagSection &Tag,unsigned long long Offset)
       unsigned long long Dist = Offset - d->iOffset;
       d->Start += Dist;
       d->iOffset += Dist;
-      return Step(Tag);
+      // if we have seen the end, don't ask for more
+      if (d->Done == true)
+	 return Tag.Scan(d->Start, d->End - d->Start);
+      else
+	 return Step(Tag);
    }
 
    // Reposition and reload..

test/integration/test-apt-get-source-multisources

@@ -0,0 +1,30 @@
+#!/bin/sh
+set -e
+
+TESTDIR=$(readlink -f $(dirname $0))
+. $TESTDIR/framework
+
+setupenvironment
+configarchitecture 'armhf'
+
+insertsource 'unstable' 'adduser' 'all' '3.113+nmu3'
+insertsource 'stable' 'python-fll' 'all' '0.9.11'
+
+insertpackage 'unstable' 'adduser' 'all' '3.113+nmu3'
+insertpackage 'stable' 'python-fll' 'all' '0.9.11'
+
+setupaptarchive
+
+APTARCHIVE=$(readlink -f ./aptarchive)
+
+HEADER="Reading package lists...
+Building dependency tree..."
+testequal "$HEADER
+Need to get 0 B of source archives.
+'file://${APTARCHIVE}/adduser_3.113+nmu3.dsc' adduser_3.113+nmu3.dsc 0 MD5Sum:d41d8cd98f00b204e9800998ecf8427e
+'file://${APTARCHIVE}/python-fll_0.9.11.dsc' python-fll_0.9.11.dsc 0 MD5Sum:d41d8cd98f00b204e9800998ecf8427e" aptget source -qdy --print-uris --dsc-only adduser=3.113 python-fll=0.9.11
+
+testequal "$HEADER
+Need to get 0 B of source archives.
+'file://${APTARCHIVE}/python-fll_0.9.11.dsc' python-fll_0.9.11.dsc 0 MD5Sum:d41d8cd98f00b204e9800998ecf8427e
+'file://${APTARCHIVE}/adduser_3.113+nmu3.dsc' adduser_3.113+nmu3.dsc 0 MD5Sum:d41d8cd98f00b204e9800998ecf8427e"  aptget source -qdy --print-uris --dsc-only python-fll=0.9.11 adduser=3.113