[gnome-ostree] ostbuild: Don't crash if there's no current revision either

[Colin Walters <walters src gnome org>]

commit 2098d5263274190d5dc404028d1f0d37df945a5b
Author: Colin Walters <walters verbum org>
Date:   Fri Aug 24 17:18:36 2012 -0400

    ostbuild: Don't crash if there's no current revision either
    
    For example if the user set local:

 src/ostbuild/pyostbuild/builtin_build.py |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/ostbuild/pyostbuild/builtin_build.py b/src/ostbuild/pyostbuild/builtin_build.py
index 152359d..b37b956 100755
--- a/src/ostbuild/pyostbuild/builtin_build.py
+++ b/src/ostbuild/pyostbuild/builtin_build.py
@@ -65,7 +65,7 @@ class OstbuildBuild(builtins.Builtin):
 
     def _analyze_build_failure(self, architecture, component, component_srcdir,
                                current_vcs_version, previous_vcs_version):
-        if previous_vcs_version is not None:
+        if (current_vcs_version is not None and previous_vcs_version is not None):
             git_args = ['git', 'log', '--format=short']
             git_args.append(previous_vcs_version + '...' + current_vcs_version)
             subproc_env = dict(os.environ)