FastVector: fix stack read overrun in ensure_capacity mSize should not be set until *after* calling ensure_capacity, otherwise we will read past the end of our statically allocated buffer when initializing the new array. This was caught by AddressSanitizer during one of the Vulkan BasicDraw tests, when compiling a shader to SPIR-V. Bug: angleproject:6600 Change-Id: I9ddb326d03ce5cda23973110e63d30b8829da2f6 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3235901 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>