drop empty panels from bar width calculation (#5633)

Author: teunbrand

R/geom-bar.R

@@ -145,7 +145,7 @@ GeomBar <- ggproto("GeomBar", GeomRect,
     data <- flip_data(data, params$flipped_aes)
     data$width <- data$width %||%
       params$width %||% (min(vapply(
-        split(data$x, data$PANEL),
+        split(data$x, data$PANEL, drop = TRUE),
         resolution, numeric(1), zero = FALSE
       )) * 0.9)
     data$just <- params$just %||% 0.5