[PATCH] runqueue: Add message to explain the problem if diffsigs multiple tasks don't exist

[Richard Purdie <richard.purdie@linuxfoundation.org>]

I've run into this and the lack of output when this happens 
is confusing.

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

diff --git a/bitbake/lib/bb/runqueue.py b/bitbake/lib/bb/runqueue.py
index 8544f36..52bb12f 100644
--- a/bitbake/lib/bb/runqueue.py
+++ b/bitbake/lib/bb/runqueue.py
@@ -1298,6 +1298,8 @@ class RunQueue:
                 prevh = __find_md5__.search(latestmatch).group(0)
                 output = bb.siggen.compare_sigfiles(latestmatch, match, recursecb)
                 bb.plain("\nTask %s:%s couldn't be used from the cache because:\n  We need hash %s, closest matching task was %s\n  " % (pn, taskname, h, prevh) + '\n  '.join(output))
+            else:
+                bb.plain("Error, can't find multiple tasks at divergence point? Was there a previously run task?")
 
 class RunQueueExecute: