Keep Placed Receivers Only

[davschneller]

To help with #53. It does the following:

• if a receiver is not mapped, it is not going to be written to the output (that is a change compared to Allow per-receiver depth #8 )
• if we start with 0 receivers, we quit immediately

[Thomas-Ulrich]

it works, now, thanks!

di73yeq4@login03:/hppfs/scratch/0A/di73yeq4/issue_receivers> /hppfs/work/pr45fi/di73yeq4/Meshing/place_receivers/build/place_receivers -d 1 -r tmp/seissol_station.txt -m tmp/mesh.puml.h5 -o tmp/seissol_station_placed.txt
Read 18 receivers.
Thu Jan 09 08:47:46, Info:  Found 460084 cells 
Thu Jan 09 08:47:46, Info:  Found 77088 vertices 
Processing partition 0 to 1
Warning: Did not find elevation for receiver at (10160.1, -210086).
Warning: Did not find elevation for receiver at (-19353.5, -238241).
Warning: Did not find elevation for receiver at (-19399.4, -238440).
Warning: Did not find elevation for receiver at (-28644.8, -257049).
Warning: Did not find elevation for receiver at (-167630, -243838).
Warning: Did not find elevation for receiver at (-108221, -271438).
Warning: Did not find elevation for receiver at (-132005, -286114).
Warning: Did not find elevation for receiver at (194990, -202003).
Warning: Did not find elevation for receiver at (-158542, -307681).
Warning: Did not find elevation for receiver at (196596, -211967).
Warning: Did not find elevation for receiver at (-179187, -307303).
Warning: Did not find elevation for receiver at (181214, -233287).
Warning: Did not find elevation for receiver at (153507, -260791).
Warning: Did not find elevation for receiver at (86204.5, -312418).
14 points were not written due to missing elevation.

[Thomas-Ulrich]

LGTM