zip_source_seek: fix EOF status after successful seek.

From Michael Beck.
diff --git a/lib/zip_source_seek.c b/lib/zip_source_seek.c
index aed53b8..4a71bfb 100644
--- a/lib/zip_source_seek.c
+++ b/lib/zip_source_seek.c
@@ -50,7 +50,12 @@
     args.offset = offset;
     args.whence = whence;
 
-    return (_zip_source_call(src, &args, sizeof(args), ZIP_SOURCE_SEEK) < 0 ? -1 : 0);
+    if (_zip_source_call(src, &args, sizeof(args), ZIP_SOURCE_SEEK) < 0) {
+	return -1;
+    }
+
+    src->eof = 0;
+    return 0;
 }