best-caf-kernel: return 0 if no tags are found

* ´git tag -l <tag>´ returns "" if no tags are found

Change-Id: Ia79db1c8978579efe56de26968124888463ae7ca

best-caf-kernel/best-caf-kernel.py

@@ -30,6 +30,9 @@ def run_subprocess(cmd):
 def get_tags(tag_name):
     cmd = "git tag -l %s" % tag_name
     comm = run_subprocess(cmd)
+    if not str(comm[0]):
+        return 0
+
     return comm[0].strip("\n").split("\n")