client: input: fix cl_movespeedkey handling

[Vladislav4KZ]

Fixes: #109

Match the original CS 1.6 client behavior by moving IN_Move before the maxspeed clamp, applying cl_movespeedkey after the clamp, and capping the multiplier at 0.52.

Remove the additional cl_movespeedkey multiplication from IN_Move to avoid applying the multiplier twice.

Pseudocode from the original Steam version of CS 1.6, decompiled from client.so using IDA Pro

IN_Move(frametime, cmd);
v48 = gEngfuncs.GetClientMaxspeed();
if ( v48 != 0.0 )
{
  v64 = sqrt(cmd->forwardmove * cmd->forwardmove + cmd->sidemove * cmd->sidemove + cmd->upmove * cmd->upmove);
  if ( v64 > v48 )
  {
	v65 = v48 / v64;
	cmd->forwardmove = cmd->forwardmove * v65;
	cmd->sidemove = cmd->sidemove * v65;
	cmd->upmove = v65 * cmd->upmove;
  }
}
if ( (in_speed.state & 1) != 0 )
{
  v49 = cl_movespeedkey->value;
  if ( v49 > 0.51999998 )
	v49 = 0.51999998;
  cmd->forwardmove = cmd->forwardmove * v49;
  cmd->sidemove = cmd->sidemove * v49;
  cmd->upmove = v49 * cmd->upmove;
}