SH-1815 Fix for crash when using old version slm

indra/llprimitive/llmodel.cpp

@@ -1784,6 +1784,7 @@ bool LLModel::loadModel(std::istream& is)
 	if (header[nm[lod]]["offset"].asInteger() == -1 || 
 		header[nm[lod]]["size"].asInteger() == 0 )
 	{ //cannot load requested LOD
+		llwarns << "LoD data is invalid!" << llendl;
 		return false;
 	}
 
@@ -1844,6 +1845,10 @@ bool LLModel::loadModel(std::istream& is)
 		}
 		return true;
 	}
+	else
+	{
+		llwarns << "unpackVolumeFaces failed!" << llendl;
+	}
 
 	return false;
 

indra/newview/llfloatermodelpreview.cpp

@@ -1970,7 +1970,7 @@ bool LLModelLoader::loadFromSLM(const std::string& filename)
 			}
 			else
 			{
-				llassert(model[lod].empty());
+				return false;
 			}
 		}
 	}