Merging surfaces also fixes the header vertex count and face count

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: ieegio
 Title: File IO for Intracranial Electroencephalography
-Version: 0.0.3.9001
+Version: 0.0.3.9002
 Language: en-US
 Encoding: UTF-8
 Authors@R: 

R/aaa-generics-surface.R

@@ -283,6 +283,29 @@ fix_surface_class <- function(x) {
   cls <- class(x)
   cls <- c(contain_classes, cls[!cls %in% remove_classes])
   class(x) <- unique(cls)
+
+  # also fix the internal header
+  if("ieegio_surface_contains_geometry" %in% contain_classes) {
+    geometry <- .subset2(x, "geometry")
+    nverts <- ncol(geometry$vertices)
+    if(length(geometry$faces)) {
+      type <- "tris"
+      nfaces <- ncol(geometry$faces)
+    } else {
+      type <- "points"
+      nfaces <- 0L
+    }
+    x$header <- structure(
+      class = "basic_geometry",
+      list(
+        internal = list(
+          num_vertices_expected = nverts,
+          num_faces_expected = nfaces
+        ),
+        mesh_face_type = type
+      )
+    )
+  }
   x
 }
 
@@ -465,8 +488,6 @@ merge.ieegio_surface <- function(
   # make dense x and make sure face starts from 1
   x <- sparse_to_dense_geometry(x)
 
-  x_matrix_world <- x$geometry$transforms
-
   get_transform <- function(z, idx) {
     transforms <- z$geometry$transforms
     if(is.na(idx) || !length(transforms)) {