Feature request: org-agenda-clockreport-mode to omit files with no clocked time

[Stig Brautaset <stig@brautaset.org>]

Hello,

I often end up with empty files in my org-agenda-clockreport-mode,
something like this. (For the avoidance of doubt: this is an ECM ;-) )

| File         | Headline         | Time   |   |
|--------------+------------------+--------+---|
|              | ALL *Total time* | *0:42* |   |
|--------------+------------------+--------+---|
| maybe.org    | *File time*      | *0:00* |   |
|--------------+------------------+--------+---|
| projects.org | *File time*      | *0:00* |   |
|--------------+------------------+--------+---|
| tasks.org    | *File time*      | *0:42* |   |
|              | Foo              | 0:08   |   |
|              | Bar              | 0:24   |   |
|              | Quux             | 0:10   |   |

I would have liked it to hide all the uninteresting files (i.e. files
with no clocked time) and instead shown me:


| File         | Headline         | Time   |   |
|--------------+------------------+--------+---|
|              | ALL *Total time* | *0:42* |   |
|--------------+------------------+--------+---|
| tasks.org    | *File time*      | *0:42* |   |
|              | Foo              | 0:08   |   |
|              | Bar              | 0:24   |   |
|              | Quux             | 0:10   |   |

It seems like a small-ish change I may brave to implement--unless
someone beats me to it, which I'm fine with! I would appreciate some
pointers:

1. Would I need to introduce an option, in case anyone relies on the
   empty sections? (I *think* not, as I gather the prevailing wind is to
   reduce the number of options.)
2. Would this likely be best implemented as a post-processing filter? Or
   when generating the table in the first place?
3. Any helpful hints you can think of? :-)


Stig