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Pickup measure becomes measure 0

Trying to insert any key / meter / tempo / band change at the pickup measure produces a zeroth measure. The end measure number’s editbox is also unconstrained.

The fix is to simply not allow changes on measure 0 (or 1 if the pickup is absent, so that the minimum value would be 2 in that case), because any changes on the first bar are automatically synchronized with the project’s initial settings anyway.