Fix for solver issue pointed out by @moskewcz in #1972

Use ReadNetParamsFromBinaryFileOrDie to read a net param when restoring
from a saved solverstate, which upgrades old nets, rather than
ReadProtoFromBinaryFile.

src/caffe/solver.cpp

@@ -349,7 +349,7 @@ void Solver<Dtype>::Restore(const char* state_file) {
   NetParameter net_param;
   ReadProtoFromBinaryFile(state_file, &state);
   if (state.has_learned_net()) {
-    ReadProtoFromBinaryFile(state.learned_net().c_str(), &net_param);
+    ReadNetParamsFromBinaryFileOrDie(state.learned_net().c_str(), &net_param);
     net_->CopyTrainedLayersFrom(net_param);
   }
   iter_ = state.iter();