pmShutterCorrection members not assigned if guess fails causing seg fault

[giebink]

In pmShutterReference (shutterCorrection.c) the call to pmShutterCorrectionFullFit has as an argument the guess returned by the preceding call to pmShutterCorrectionGuess. However, failures in pmShutterCorrectionGuess transfer control to GUESS_ERROR via a goto. At GUESS_ERROR memory is freed but pmShutterCorrection struct members scale, offset, and offref are not assigned. This cause a seg fault when the values are accessed.

[eugene]

Looks like pmShutterCorrectionFullFit now checks for a NULL guess and returns NULL, and the calling function (pmShutterCorrectionMeasure) likewise returns a NULL on a NULL return from pmShutterCorrectionFullFit.

the psTrace after the call to pmShutterCorrectionFullFit in pmShutterCorrectionReference was not protected. This is now only called if the return value is not NULL.

(r27832)