repo: Autofree contents of input_mfile

Coverity points out that we have memory leak from
g_mapped_file_get_contents(input_mfile).

src/libostree/ostree-repo-static-delta-processing.c

@@ -423,10 +423,11 @@ dispatch_bspatch (OstreeRepo *repo, StaticDeltaExecutionState *state, GCancellab
       struct bspatch_stream stream;
       stream.read = bspatch_read;
       stream.opaque = &opaque;
-      if (bspatch ((const guint8 *)g_mapped_file_get_contents (input_mfile),
-                   g_mapped_file_get_length (input_mfile), buf, state->content_size, &stream)
+      g_autofree const guint8 *old = (const guint8 *)g_mapped_file_get_contents (input_mfile);
+      if (bspatch (old, g_mapped_file_get_length (input_mfile), buf,
+                   state->content_size, &stream)
           < 0)
-        return glnx_throw (error, "bsdiff patch failed");
+      return glnx_throw (error, "bsdiff patch failed");
 
       if (!_ostree_repo_bare_content_write (repo, &state->content_out, buf, state->content_size,
                                             cancellable, error))