arcadeDrive requires multiple calls

[ajlewis02]

drivetrain.arcadeDrive() doesn't seem to correctly set all motors unless it's called multiple times in a row.

Originally, I thought this issue had to do with calling delay() after a call to arcadeDrive() - but, the issue seems to be more correlated to whether there are multiple arcadeDrive() calls. (It's likely that it only appeared to have to do with the delay() call because, under other circumstances, arcadeDrive() is called multiple times because the loop function is called multiple times.)

This issue is most easily observed when writing an auto mode, because some auto mode implementations perform the entire auto mode with only one call of the loop function.

Within a single call of the loop function the pattern:

drivetrain.arcadeDrive(-1, 0);
delay(1000);

doesn't set all motors. Its behavior varies between runs - sometimes, three motors are set, and sometimes two motors are set.

However, if the above block of code is run twice in a row (such as by holding down the "auto begin" button), all motors are correctly set on the second run.

These patterns both work as expected:

drivetrain.arcadeDrive(-1,0);
drivetrain.arcadeDrive(-1,0);
delay(1000);

drivetrain.arcadeDrive(0,0);
drivetrain.arcadeDrive(-1,0);
delay(1000);