Fix MPI variable in utilities.cc from int to unsigned int.

Author: MFraters

source/world_builder/utilities.cc

@@ -1183,14 +1183,14 @@ namespace WorldBuilder
           MPI_Comm_rank(comm, &my_rank);
           if (my_rank == 0)
             {
-              int filesize;
+              unsigned int filesize;
               std::ifstream filestream;
               filestream.open(filename.c_str());
               WBAssertThrow (filestream.is_open(), std::string("Could not open file <") + filename + ">.");
 
               // Need to convert to unsigned int, because MPI_Bcast does not support
               // size_t or const unsigned int
-              int invalid_file_size = -1;
+              unsigned int invalid_file_size = -1;
 
               if (!filestream)
                 {