BLI_path: add BLI_path_normalize_native for non-blend file paths

System paths with multiple leading slashes get normalized to one slash.

source/blender/blenlib/BLI_path_util.h

@@ -155,6 +155,14 @@ void BLI_path_to_display_name(char *display_name, int display_name_maxncpy, cons
  * \param path: The path to a file or directory which can be absolute or relative.
  */
 void BLI_path_normalize(char *path) ATTR_NONNULL(1);
+
+/**
+ * A version of #BLI_path_normalize without special handling of `//` blend file relative prefix.
+ *
+ * \note On UNIX `//path` is a valid path which gets normalized to `/path`.
+ */
+void BLI_path_normalize_native(char *path) ATTR_NONNULL(1);
+
 /**
  * Cleanup file-path ensuring a trailing slash.
  *

source/blender/blenlib/intern/path_util.c

@@ -135,7 +135,7 @@ void BLI_path_sequence_encode(char *path,
   BLI_snprintf(path, path_maxncpy, "%s%.*d%s", head, numlen, MAX2(0, pic), tail);
 }
 
-void BLI_path_normalize(char *path)
+static void path_normalize_impl(char *path, bool check_blend_relative_prefix)
 {
   const char *path_orig = path;
   int path_len = strlen(path);
@@ -144,7 +144,7 @@ void BLI_path_normalize(char *path)
    * Skip absolute prefix.
    * ---------------------
    */
-  if (path[0] == '/' && path[1] == '/') {
+  if (check_blend_relative_prefix && (path[0] == '/' && path[1] == '/')) {
     path = path + 2; /* Leave the initial `//` untouched. */
     path_len -= 2;
 
@@ -357,6 +357,16 @@ void BLI_path_normalize(char *path)
 #undef IS_PARENT_DIR
 }
 
+void BLI_path_normalize(char *path)
+{
+  path_normalize_impl(path, true);
+}
+
+void BLI_path_normalize_native(char *path)
+{
+  path_normalize_impl(path, false);
+}
+
 void BLI_path_normalize_dir(char *dir, size_t dir_maxncpy)
 {
   /* Would just create an unexpected "/" path, just early exit entirely. */