[Release] releases.py should not crash on non-release versions

tools/release/releases.py

 #!/usr/bin/env python
 # Copyright 2014 the V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # This script retrieves the history of all V8 branches and
 # their corresponding Chromium revisions.
 
 # Requires a chromium checkout with branch heads:
 # gclient sync --with_branch_heads
@@ skipping 445 matching lines @@
 
         current_candidate = self._CreateCandidate(current_version)
         canaries.append(current_candidate)
 
     chrome_releases = {"canaries": canaries}
     self["chrome_releases"] = chrome_releases
 
   def _GetGitHashForV8Version(self, v8_version):
     if v8_version == "N/A":
       return ""
+
+    real_v8_version = v8_version
     if v8_version.split(".")[3]== "0":
-      return self.GitGetHashOfTag(v8_version[:-2])
+      real_v8_version = v8_version[:-2]
 
-    return self.GitGetHashOfTag(v8_version)
+    try:
+      return self.GitGetHashOfTag(real_v8_version)
+    except GitFailedException:
+      return ""
 
   def _CreateCandidate(self, current_version):
     params = None
     url_to_call = (OMAHA_PROXY_URL + "v8.json?version="
                    + current_version["previous_version"])
     result_raw = self.ReadURL(
                          url_to_call,
                          params,
                          wait_plan=[5, 20]
                          )
@@ skipping 82 matching lines @@
       RetrieveChromiumV8Releases,
       RetrieveChromiumBranches,
       RetrieveInformationOnChromeReleases,
       CleanUp,
       WriteOutput,
     ]
 
 
 if __name__ == "__main__":  # pragma: no cover
   sys.exit(Releases().Run())