#40 GRAB SET_NEAR does not handle irregular keys

[seismick]

The process GRAB is used to write statics values and read them back. If the HDR_A is receiver station, this is usually incrementing by 1 or otherwise regular. With OPT_MODE = SET_NEAR, it works. However, if you are dealing with
shot statics, and are keying them by FFID, this might be irregular, especially
with old seismic data. Possible problems include the file number being octal
so it jumps from 7 to 10 then 77 to 100 and so on. Or it might rollover from 999
to 000. And often the observer did not set the file number consistently when
moving recorder, so file number might jump by 100 or 1000 arbitrarily.
So when using SET_NEAR with an irregular key, I have seen the first few shots
having the wrong static set, which is the same value in these first shots.

I discovered a workaround: it sets the correct statics if you pad the start of
the XML file with several dummy lines before the first shot
(e.g. N-4, N-3, N-2 and N-1 where N is first shot).
These would go after the line

xcoord ycoord static 1 1