[Bugfix] Corrected zooming in/out command handler

If you bind zoom in/out commands to keys and then try to use zoom, you will find that zooming works incorrectly. Game would switch 2 zoomsteps per 1 keypress. It happens because the handler changes zoomstep twice: when you press the key and when you release it.
Fix makes zoomstep changing only when key is pressed, not released.

src/xrGame/Weapon.cpp

@@ -968,7 +968,7 @@ bool CWeapon::Action(u16 cmd, u32 flags)
 
     case kWPN_ZOOM_INC:
     case kWPN_ZOOM_DEC:
-        if (IsZoomEnabled() && IsZoomed())
+        if (IsZoomEnabled() && IsZoomed() && (flags&CMD_START) )
         {
             if (cmd == kWPN_ZOOM_INC)
                 ZoomInc();