ir_constant: Don't crash on out-of-bounds vector/matrix accesses

Danylo Piliaiev requested to merge GL/mesa:fix/oob-access-to-vector into master

Several optimization paths, including constant folding, can lead to accessing an ir_constant vector/matrix with an out of bounds index. The GLSL spec lets us produce "undefined" results, but it does not let us crash.

Similar to 66436405

Closes: #2604 (closed)

Piglit tests: piglit!238 (merged)

Edited by Danylo Piliaiev

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