Fixes an optimization bug producing #INF in the egg file. Added check to make sure data isn't empty. This might be an issue only found in VS2008 SP1.

panda/src/egg/eggSAnimData.cxx

@@ -39,7 +39,9 @@ optimize() {
     }
 
     // Ok, all the rows had the same value.  Collapse them.
-    _data.erase(_data.begin() + 1, _data.end());
+	if(!_data.empty()){
+		_data.erase(_data.begin() + 1, _data.end());
+	}
   }
 }