early out compute_point_to_point_communication_pattern()

Fixes another stl invalid access

diff --git a/source/base/mpi.cc b/source/base/mpi.cc
index cd69c9c358fb1793b484d041cd2e260357486bd8..28a575330fd29e8af8b295871f1c9534e1911dde 100644 (file)
--- a/source/base/mpi.cc
+++ b/source/base/mpi.cc
@@ -141,6 +141,10 @@ namespace Utilities
       const unsigned int max_n_destinations
         = Utilities::MPI::max (destinations.size(), mpi_comm);
 
+      if (max_n_destinations==0)
+        // all processes have nothing to send/receive:
+        return std::vector<unsigned int>();
+
       // now that we know the number
       // of data packets every
       // processor wants to send, set