fallbacksrc: Misc fixes
fallbacksrc: Fix for imagefreeze framerate setup
Put imagefreeze before capsfilter so that user specified framerate
for fallback image can be applied as expected
fallbacksrc: Drop QoS event while pad is blocked
An element which creates QoS event might reference different
GstSegment timeline (e.g., fallback testsrc's one).
Then it can cause lots of buffers are being dropped in decoder,
because of the QoS events.
Drops the QoS event before we calculate appropriate pad offsets
from blocking pad probe.