bugfixes: grouping and missing libArchive (#4718)

usermods/user_fx/library.json

@@ -1,3 +1,4 @@
 {
-  "name": "user_fx"
-}
+  "name": "user_fx",
+  "build": { "libArchive": false }
+}

wled00/FX_fcn.cpp

@@ -1459,7 +1459,8 @@ void WS2812FX::blendSegment(const Segment &topSegment) const {
         const int maxX = std::min(x + topSegment.grouping, width);
         const int maxY = std::min(y + topSegment.grouping, height);
         while (y < maxY) {
-          while (x < maxX) setMirroredPixel(x++, y, c_a, opacity);
+          int _x = x;
+          while (_x < maxX) setMirroredPixel(_x++, y, c_a, opacity);
           y++;
         }
       }