* make sure maxColorAttachments is greater than 0
* Do not sync read buffer if maxDrawBuffers is 0

Bug: chromium:1167731
Change-Id: Icd0fb5e65ec6ffdc0d6f6325ccd1207958922254
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2733268Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Peng Huang <penghuang@chromium.org>