prevent drawLine from drawing out of bounds

the "smooth" variant was sometimes producing XY positions outside the canvas.

wled00/FX_2Dfcn.cpp

@@ -806,8 +806,13 @@ void Segment::drawLine(uint16_t x0, uint16_t y0, uint16_t x1, uint16_t y1, uint3
       int y = int(intersectY);
       if (steep) std::swap(x,y);  // temporarily swap if steep
       // pixel coverage is determined by fractional part of y co-ordinate
-      setPixelColorXY(x, y, color_blend(c, getPixelColorXY(x, y), keep, true));
-      setPixelColorXY(x+int(steep), y+int(!steep), color_blend(c, getPixelColorXY(x+int(steep), y+int(!steep)), seep, true));
+
+      // WLEDMM added out-of-bounds check: "unsigned(x) < cols" catches negative numbers _and_ too large values
+      if ((unsigned(x) < unsigned(cols)) && (unsigned(y) < unsigned(rows)))   setPixelColorXY(x, y, color_blend(c, getPixelColorXY(x, y), keep, true));
+      int xx = x+int(steep);
+      int yy = y+int(!steep);
+      if ((unsigned(xx) < unsigned(cols)) && (unsigned(yy) < unsigned(rows))) setPixelColorXY(xx, yy, color_blend(c, getPixelColorXY(xx, yy), seep, true));
+
       intersectY += gradient;
       if (steep) std::swap(x,y);  // restore if steep
     }