Throw when JSON Patch remove's target path resolves through a primitive or null parent

RFC 6902 (section 4.2) requires the target location of a "remove"
operation to exist. operation_remove handled parent.is_object() and
parent.is_array(), but had no final else branch: when the resolved
parent was a primitive value or null, neither branch matched and the
operation silently did nothing instead of failing.

Add the missing else branch, throwing out_of_range.413 with wording
that matches the existing out_of_range.411 thrown by the analogous
"add" case (operation_add) for the same kind of invalid parent.

Fixes #5396.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

include/nlohmann/json.hpp

@@ -4939,6 +4939,12 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
                 // note erase performs range check
                 parent.erase(json_pointer::template array_index<basic_json_t>(last_path));
             }
+            else
+            {
+                // the parent of a "remove" target must be an object or array
+                // (see #5396)
+                JSON_THROW(out_of_range::create(413, detail::concat("cannot remove value: the JSON Patch 'remove' target's parent is of type ", parent.type_name(), ", but must be an object or array"), &parent));
+            }
         };
 
         // type check: top level value must be an array