External SAT back-end: handle whitespace at end of line gracefully

CryptoMiniSat produces assignment output that includes whitespace at the
end of the line. Strip such (empty) elements before evaluating entries
as literals.

Fixes: diffblue#7164

Author: tautschnig

src/solvers/sat/external_sat.cpp

@@ -109,7 +109,7 @@ external_satt::resultt external_satt::parse_result(std::string solver_output)
 
     if(line[0] == 'v')
     {
-      auto assignments = split_string(line, ' ');
+      auto assignments = split_string(line, ' ', false, true);
 
       // remove the first element which should be 'v' identifying
       // the line as the satisfying assignments