BLI_path: add BLI_path_slash_skip utility function

Avoids having to add inline loops that step over slashes.

source/blender/blenlib/BLI_path_util.h

@@ -265,6 +265,10 @@ int BLI_path_slash_ensure(char *path, size_t path_maxncpy) ATTR_NONNULL(1);
  * Removes the last slash and everything after it to the end of path, if there is one.
  */
 void BLI_path_slash_rstrip(char *path) ATTR_NONNULL(1);
+/**
+ * \return the next non-slash character or the null byte (when `path` only contains slashes).
+ */
+const char *BLI_path_slash_skip(const char *path) ATTR_NONNULL(1) ATTR_WARN_UNUSED_RESULT;
 /**
  * Changes to the path separators to the native ones for this OS.
  */

source/blender/blenlib/intern/path_util.c

@@ -1118,9 +1118,7 @@ bool BLI_path_abs(char path[FILE_MAX], const char *basepath)
     BLI_assert(strlen(tmp) == root_dir_len);
 
     /* Step over the slashes at the beginning of the path. */
-    while (BLI_path_slash_is_native_compat(*p)) {
-      p++;
-    }
+    p = (char *)BLI_path_slash_skip(p);
     BLI_strncpy(tmp + root_dir_len, p, sizeof(tmp) - root_dir_len);
   }
   else {
@@ -1958,6 +1956,15 @@ void BLI_path_slash_rstrip(char *path)
   }
 }
 
+const char *BLI_path_slash_skip(const char *path)
+{
+  /* This accounts for a null byte too. */
+  while (BLI_path_slash_is_native_compat(*path)) {
+    path++;
+  }
+  return path;
+}
+
 void BLI_path_slash_native(char *path)
 {
 #ifdef WIN32