[b2b_entitites] Fix crash on empty To display name.

As the To display name may be empty and the DB does not enforce a not NULL, better be ready to read a NULL.
This happens when using db_cachedb + cachedb_mongodb as backend
Closes #1606

(cherry picked from commit 68aaa20)

modules/b2b_entities/b2be_db.c

@@ -498,7 +498,7 @@ int b2b_entities_restore(void)
 			dlg.from_uri.s       = (char*)row_vals[5].val.string_val;
 			dlg.from_uri.len     = strlen(dlg.from_uri.s);
 			dlg.from_dname.s     = (char*)row_vals[6].val.string_val;
-			dlg.from_dname.len   = strlen(dlg.from_dname.s);
+			dlg.from_dname.len   = dlg.from_dname.s?strlen(dlg.from_dname.s):0;
 			dlg.to_uri.s         = (char*)row_vals[7].val.string_val;
 			dlg.to_uri.len       = strlen(dlg.to_uri.s);
 			dlg.to_dname.s       = (char*)row_vals[8].val.string_val;
@@ -519,7 +519,7 @@ int b2b_entities_restore(void)
 			dlg.last_reply_code  = row_vals[17].val.int_val;
 			dlg.last_invite_cseq = row_vals[18].val.int_val;
 			dlg.param.s          = (char*)row_vals[12].val.string_val;
-			dlg.param.len        = strlen(dlg.param.s);
+			dlg.param.len        = dlg.param.s?strlen(dlg.param.s):0;
 			sockinfo_str.s       = (char*)row_vals[11].val.string_val;
 			if(sockinfo_str.s)
 			{