BUGFIX in oscillate FX (wled#4494)

effect was changed from int to uint but it relied on negative numbers. fixed by checking overflow and a cast.

Author: DedeHai

wled00/FX.cpp

@@ -1877,7 +1877,7 @@ uint16_t mode_oscillate(void) {
     uint32_t color = BLACK;
     for (unsigned j = 0; j < numOscillators; j++) {
       if((int)i >= (int)oscillators[j].pos - oscillators[j].size && i <= oscillators[j].pos + oscillators[j].size) {
-        color = (color == BLACK) ? SEGCOLOR(j) : color_blend(color, SEGCOLOR(j), 128);
+        color = (color == BLACK) ? SEGCOLOR(j) : color_blend(color, SEGCOLOR(j), uint8_t(128));
       }
     }
     SEGMENT.setPixelColor(i, color);