Crash if BC does not contain 4 elements

[reox]

file: unitcyl.h5 tolerance: 1e-06 max. num. level: 6
 Generatin mesh.... 
 compute dimension.... using cores in x: 1 in y: 2 in z: 2
Image has following dimension: 40 400 60
Time for Reading the Image: avg: 0.00324175 min: 0.003238 max: 0.003246s
Time for Reading BC: avg: 0.0011305 min: 0.00112 max: 0.001159s

HDF5 ImageReader: 
  global Dimension: 60 400 40
  local Dimension: 60 200 20 Resolution: 0.5
  Poison's ratio: 0.3
  BC: Fixednodesize: 7503 loadednodesize 1463
Refinement steps: 13
Number of Buckets: 261
Average eleme per cpu: 257481
Time for Read in: avg: 0.262409 min: 0.262111 max: 0.262575s
Nr. of global elements: 960000 global nodes: 1002901
Error! index of BC not found!
Error! index of BC not found!
Error! index of BC not found!
Error! index of BC not found!
Error! index of BC not found!
[helios:31892] *** Process received signal ***
[helios:31892] Signal: Segmentation fault (11)
[helios:31892] Signal code: Address not mapped (1)
[helios:31892] Failing at address: 0x55b1124a3020
Error! index of BC not found!
[helios:31892] [ 0] /lib/x86_64-linux-gnu/libpthread.so.0(+0x123b0)[0x7f1c5eaa03b0]
[helios:31892] [ 1] parosol(_ZN10OctreeGridI16OctreeKey_LookupE10GenerateBCEv+0x3d9)[0x55a111373229]
[helios:31892] [ 2] parosol(main+0x1355)[0x55a111358e95]
[helios:31892] [ 3] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf1)[0x7f1c5e70b561]
[helios:31892] [ 4] parosol(_start+0x2a)[0x55a11135a15a]
Error! index of BC not found!
Error! index of BC not found!
[helios:31893] *** Process received signal ***
[helios:31893] Signal: Segmentation fault (11)
[helios:31893] Signal code: Address not mapped (1)
[helios:31893] Failing at address: 0x55df64a0c6d0
[helios:31892] *** End of error message ***
[helios:31893] [ 0] /lib/x86_64-linux-gnu/libpthread.so.0(+0x123b0)[0x7f3d79a4b3b0]
[helios:31893] [ 1] parosol(_ZN10OctreeGridI16OctreeKey_LookupE10GenerateBCEv+0x3d9)[0x55cf641fd229]
[helios:31893] [ 2] parosol(main+0x1355)[0xError! index of BC not found!
55cf641e2e95[helios:31891] *** Process received signal ***
]
[helios:31891] Signal: Segmentation fault (11)
[helios:31891] Signal code: Address not mapped (1)
[helios:31891] Failing at address: 0x55746778d540
[helios:31893] [ 3] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf1)[0x7f3d796b6561]
[helios:31893] [ 4] parosol(_start+0x2a)[0x55cf641e415a]
[helios:31893] *** End of error message ***
[helios:31891] [ 0] /lib/x86_64-linux-gnu/libpthread.so.0(+0x123b0)[0x7fa0090323b0]
[helios:31891] [ 1] parosol(_ZN10OctreeGridI16OctreeKey_LookupE10GenerateBCEv+0x3d9)[0x5564654f2229]
[helios:31891] [ 2] parosol(main+0x1355)[0x5564654d7e95]
[helios:31891] [ 3] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf1)[0x7fa008c9d561]
[helios:31891] [ 4] parosol(_start+0x2a)[0x5564654d915a]
[helios:31891] *** End of error message ***
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mpirun noticed that process rank 1 with PID 0 on node helios exited on signal 11 (Segmentation fault).
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But only if multiprocessing is used!