oeqa/utils/dump: Handle empty commandlist gracefully

If the commandlist isn't available, the code currently gives a backtrace.
At least stop doing that and return more gracefully.

(From OE-Core rev: e6903e9ef856d98258d81587bf85199cb7dbdca4)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/utils/dump.py

@@ -14,6 +14,8 @@ class BaseDumper(object):
     def __init__(self, d, cmds):
         self.cmds = []
         self.parent_dir = d.getVar("TESTIMAGE_DUMP_DIR", True)
+        if not cmds:
+            return
         for cmd in cmds.split('\n'):
             cmd = cmd.lstrip()
             if not cmd or cmd[0] == '#':