Fix DefaultCastRegisterer<std::string>::cast

  - when signal value contained a space, only the part before the space
    was stored in the signal.
  - add a test on this case.
8 jobs for v3.7.3 in 4 minutes and 20 seconds (queued for 1 second)
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Status Name Job ID Coverage
  Test
passed doc-coverage #40699

00:02:37

79.0%
failed format #40700
allowed to fail

00:01:51

passed robotpkg-dynamic-graph-v3-16.04-debug #40694

00:03:20

passed robotpkg-dynamic-graph-v3-16.04-release #40693

00:03:25

passed robotpkg-dynamic-graph-v3-18.04-debug #40696

00:04:00

passed robotpkg-dynamic-graph-v3-18.04-release #40695

00:04:14

passed robotpkg-dynamic-graph-v3-stretch-debug #40698

00:04:19

passed robotpkg-dynamic-graph-v3-stretch-release #40697

00:04:18

 
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format Test
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