model_loader.js : fix bug with undefined IMGT field

browser/js/model_loader.js

@@ -556,7 +556,7 @@ Model_loader.prototype = {
                     elem.eValue   = clone.eValue;
                     elem.seg      = clone.seg
                     //remove unneeded elements sometimes left after IMGT interrogation
-                    if (clone.seg.imgt["Sequence number"]!==null){
+                    if (typeof clone.seg.imgt != 'undefined' && clone.seg.imgt["Sequence number"]!==null){
                         delete clone.seg.imgt["Sequence number"];} //m.clones[i].seg.imgt["Sequence number"]
                 };