FrameCapture: Handle zero vertex count draws Seeing the following from GLES1 (note count = 0): glDrawArrays(context = 1, mode = GL_POINTS, first = 0, count = 0) This crahes in FrameCaptureShared::captureClientArraySnapshot: 'length_error was thrown in -fno-exceptions mode with message "vector"' The function assumes vertexCount will always be greater than zero. This CL updates it to detect the empty case and simply return. Negative counts are already handled as a GL error. Test: Plague Inc MEC Bug: b/321562592 Change-Id: I3613eaac297a3471dc998b023bf2658413cb5d1b Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5250427 Commit-Queue: Cody Northrop <cnorthrop@google.com> Reviewed-by: Mike Schuchardt <mikes@lunarg.com>