mkv (ebml): Fix testing if the next element is a direct child of an ancestor.

When the parent element of the current element has an unknown size,
the parent element ends if the next element is a direct child of any
ancestor of the parent. This test, performed for each ancestor, requires
the depth of the ancestor's child elements, and the ancestor's element ID.
The pre-existing test passed the depth of the ancestor and not the depth
of its children resulting in this test never passing.

Fixes #541.

Author: pdeljanov

symphonia-format-mkv/src/ebml.rs

@@ -536,7 +536,7 @@ impl<R: ReadEbml, S: EbmlSchema> EbmlIterator<R, S> {
             // parent element, then the parent element has ended. Return `None` in such a case.
             if parent_end.is_none() {
                 for ancestor in self.stack.iter().rev().skip(1) {
-                    if header.is_valid_at(ancestor.depth, ancestor.id).unwrap_or(false) {
+                    if header.is_valid_at(ancestor.depth + 1, ancestor.id).unwrap_or(false) {
                         // This element is a direct child of an ancestor. Iteration will be
                         // terminated to indicate the end of the parent element.
                         return Ok(None);