window: Use loop instead of multiple ifs
    
    Binds modifier's mask and key, also fixes a compile time warning
    spotted by clang:
     warning: cast from 'gchar *' (aka 'char *') to 'guint *' (aka 'unsigned
      int *') increases required alignment from 1 to 4 [-Wcast-align]
     return (guint*)g_array_free(a, FALSE);