fetch2: add try/finally to ensure lockfile is unlocked on failure

Signed-off-by: Saul Wold <sgw@linux.intel.com>

bitbake/lib/bb/fetch2/__init__.py

@@ -830,6 +830,7 @@ class Fetch(object):
 
             lf = bb.utils.lockfile(ud.lockfile)
 
+            try:
                 if not m.need_update(u, ud, self.d):
                     localpath = ud.localpath
                 elif m.try_premirror(u, ud, self.d):
@@ -873,6 +874,7 @@ class Fetch(object):
                     verify_checksum(u, ud, self.d)
                     open(ud.donestamp, 'w').close()
 
+            finally:
                 bb.utils.unlockfile(lf)
 
     def checkstatus(self, urls = []):