Use lineend from correct env

Fixes #1852

Author: hadley

NEWS.md

@@ -171,6 +171,8 @@ There were a number of tweaks to the theme elements that control legends:
 
 * `geom_contour()` more clearly describes what inputs it needs (#1577).
 
+* `geom_curve()` respects the `lineend` paramater (#1852).
+
 * `geom_histogram()` and `stat_bin()` understand the `breaks` parameter once 
   more. (#1665). The floating point adjustment for histogram bins is now 
   actually used - it was previously inadvertently ignored (#1651).

R/geom-curve.r

@@ -45,6 +45,7 @@ GeomCurve <- ggproto("GeomCurve", GeomSegment,
         call. = FALSE)
     }
     trans <- coord$transform(data, panel_scales)
+
     curveGrob(
       trans$x, trans$y, trans$xend, trans$yend,
       default.units = "native",
@@ -54,7 +55,7 @@ GeomCurve <- ggproto("GeomCurve", GeomSegment,
         col = alpha(trans$colour, trans$alpha),
         lwd = trans$size * .pt,
         lty = trans$linetype,
-        lineend = trans$lineend),
+        lineend = lineend),
       arrow = arrow
     )
   }