Move draw call early-outs until after validation.
Move draw call early-outs until after validation.

Drawing without a current program is not an error and we can early-out,
but not until after other validation which could generate an error has
completed. Validation happening on a valid program happens afterwards
though. Likewise, providing insufficient vertices for even one
primitive results in drawing nothing, but validation still needs to
happen.

Change-Id: I5385ffe352fc38343caa41eb99f5549472da3b4f
Reviewed-on: https://swiftshader-review.googlesource.com/14489
Tested-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>

google/swiftshader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader