patch 8.2.0916: mapping with partly modifyOtherKeys code does not work

Problem:    Mapping with partly modifyOtherKeys code does not work.
Solution:   If there is no mapping with a separate modifier include the
            modifier in the key and then try mapping again. (closes #6200)

src/edit.c

@@ -1609,7 +1609,7 @@ decodeModifyOtherKeys(int c)
 #endif
 
 	    mod_mask = decode_modifiers(arg[!form]);
-	    c = merge_modifyOtherKeys(arg[form]);
+	    c = merge_modifyOtherKeys(arg[form], &mod_mask);
 	}
     }