block: fix msg_passing/hier/ example
gr-fft-filter : Fix uninitialized pointers.

Address CID's 1043252 and 1043253. Inspection suggest the code should
work, but set the pointers to NULL to force errors on strange code
paths.

Signed-off-by: Philip Balister <philip@balister.org>
pfb-decimator : Fix leak.

Address CID 1046270.

Signed-off-by: Philip Balister <philip@balister.org>
Merge remote-tracking branch 'gnuradio-wg-grc/blocks_msg_example_fix' into maint