The crash is because mBufferFreeList is not moved from the rhs
value for DynamicBuffer's move constructor.

Bug: chromium:1170339
Change-Id: I7d41b775ab56af8fa9412369d5a4008f59da3053
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2661615Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>