fix water volume for waterfalls (LEVEL3A)

src/mesh.h

@@ -831,6 +831,8 @@ struct MeshBuilder {
         for (int i = 0; i < wVertices.length; i++) {
             short3 &v = wVertices[i];
 
+            int16 base = v.y;
+
             v.y += WATER_VOLUME_HEIGHT - WATER_VOLUME_OFFSET - WATER_VOLUME_OFFSET;
 
             const vec3 sectorOffsets[] = {
@@ -851,7 +853,9 @@ struct MeshBuilder {
 
             floor -= WATER_VOLUME_OFFSET * 3;
 
+            if (floor > base) {
                 v.y = min(v.y, floor);
+            }
 
             vertices[vCount++].coord = short4(v.x, v.y, v.z, 0);
         }