[all] Fix for helping to add new curves into open9x

src/open9x.cpp

@@ -352,7 +352,7 @@ int16_t applyCurve(int16_t x, int8_t idx)
   }
   if (idx < 0) {
     x = -x;
-    idx = -idx + 6;
+    idx = -idx + CURVE_BASE - 1;
   }
   return intpol(x, idx - 7);
 }