Consider PANEL for handling NAs in line geoms (#6541)

* consider panel as grouping structure

* add news bullet

Author: teunbrand

NEWS.md

@@ -1,5 +1,6 @@
 # ggplot2 (development version)
 
+* Fixed bug where `NA` handling in `geom_path()` was ignoring panels (@teunbrand, #6533)
 * Logical values for the linetype aesthetic will be interpreted numerically,
   so that `linetype = FALSE` becomes 0/'blank' and `linetype = TRUE` becomes 
   1/'solid' (@teunbrand, #6641)

R/geom-path.R

@@ -19,7 +19,7 @@ GeomPath <- ggproto("GeomPath", Geom,
     # middle since you expect those to be shown by a break in the line
     aesthetics <- c(self$required_aes, self$non_missing_aes)
     complete <- stats::complete.cases(data[names(data) %in% aesthetics])
-    kept <- stats::ave(complete, data$group, FUN = keep_mid_true)
+    kept <- stats::ave(complete, data$group, data$PANEL, FUN = keep_mid_true)
     data <- data[kept, ]
 
     if (!all(kept) && !params$na.rm) {